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Appendix A. Contributed Scripts

These scripts, while not fitting into the text of this document, do illustrate some interesting shell programming techniques. They are useful, too. Have fun analyzing and running them.

Example A-1. mailformat: Formatting an e-mail message

#!/bin/bash
# mail-format.sh (ver. 1.1): Format e-mail messages.

# Gets rid of carets, tabs, and also folds excessively long lines.

# =================================================================
#                 Standard Check for Script Argument(s)
ARGS=1
E_BADARGS=65
E_NOFILE=66

if [ $# -ne $ARGS ]  # Correct number of arguments passed to script?
then
  echo "Usage: `basename $0` filename"
  exit $E_BADARGS
fi

if [ -f "$1" ]       # Check if file exists.
then
    file_name=$1
else
    echo "File \"$1\" does not exist."
    exit $E_NOFILE
fi
# =================================================================

MAXWIDTH=70          # Width to fold excessively long lines to.

# ---------------------------------
# A variable can hold a sed script.
sedscript='s/^>//
s/^  *>//
s/^  *//
s/		*//'
# ---------------------------------

#  Delete carets and tabs at beginning of lines,
#+ then fold lines to $MAXWIDTH characters.
sed "$sedscript" $1 | fold -s --width=$MAXWIDTH
                        #  -s option to "fold"
                        #+ breaks lines at whitespace, if possible.


#  This script was inspired by an article in a well-known trade journal
#+ extolling a 164K MS Windows utility with similar functionality.
#
#  An nice set of text processing utilities and an efficient
#+ scripting language provide an alternative to bloated executables.

exit

Example A-2. rn: A simple-minded file renaming utility

This script is a modification of Example 15-22.

#! /bin/bash
# rn.sh

# Very simpleminded filename "rename" utility (based on "lowercase.sh").
#
#  The "ren" utility, by Vladimir Lanin (lanin@csd2.nyu.edu),
#+ does a much better job of this.


ARGS=2
E_BADARGS=85
ONE=1                     # For getting singular/plural right (see below).

if [ $# -ne "$ARGS" ]
then
  echo "Usage: `basename $0` old-pattern new-pattern"
  # As in "rn gif jpg", which renames all gif files in working directory to jpg.
  exit $E_BADARGS
fi

number=0                  # Keeps track of how many files actually renamed.


for filename in *$1*      #Traverse all matching files in directory.
do
   if [ -f "$filename" ]  # If finds match...
   then
     fname=`basename $filename`            # Strip off path.
     n=`echo $fname | sed -e "s/$1/$2/"`   # Substitute new for old in filename.
     mv $fname $n                          # Rename.
     let "number += 1"
   fi
done   

if [ "$number" -eq "$ONE" ]                # For correct grammar.
then
 echo "$number file renamed."
else 
 echo "$number files renamed."
fi 

exit $?


# Exercises:
# ---------
# What types of files will this not work on?
# How can this be fixed?

Example A-3. blank-rename: Renames filenames containing blanks

This is an even simpler-minded version of previous script.

#! /bin/bash
# blank-rename.sh
#
# Substitutes underscores for blanks in all the filenames in a directory.

ONE=1                     # For getting singular/plural right (see below).
number=0                  # Keeps track of how many files actually renamed.
FOUND=0                   # Successful return value.

for filename in *         #Traverse all files in directory.
do
     echo "$filename" | grep -q " "         #  Check whether filename
     if [ $? -eq $FOUND ]                   #+ contains space(s).
     then
       fname=$filename                      # Yes, this filename needs work.
       n=`echo $fname | sed -e "s/ /_/g"`   # Substitute underscore for blank.
       mv "$fname" "$n"                     # Do the actual renaming.
       let "number += 1"
     fi
done   

if [ "$number" -eq "$ONE" ]                 # For correct grammar.
then
 echo "$number file renamed."
else 
 echo "$number files renamed."
fi 

exit 0

Example A-4. encryptedpw: Uploading to an ftp site, using a locally encrypted password

#!/bin/bash

# Example "ex72.sh" modified to use encrypted password.

#  Note that this is still rather insecure,
#+ since the decrypted password is sent in the clear.
#  Use something like "ssh" if this is a concern.

E_BADARGS=65

if [ -z "$1" ]
then
  echo "Usage: `basename $0` filename"
  exit $E_BADARGS
fi  

Username=bozo           # Change to suit.
pword=/home/bozo/secret/password_encrypted.file
# File containing encrypted password.

Filename=`basename $1`  # Strips pathname out of file name.

Server="XXX"
Directory="YYY"         # Change above to actual server name & directory.


Password=`cruft <$pword`          # Decrypt password.
#  Uses the author's own "cruft" file encryption package,
#+ based on the classic "onetime pad" algorithm,
#+ and obtainable from:
#+ Primary-site:   ftp://ibiblio.org/pub/Linux/utils/file
#+                 cruft-0.2.tar.gz [16k]


ftp -n $Server <<End-Of-Session
user $Username $Password
binary
bell
cd $Directory
put $Filename
bye
End-Of-Session
# -n option to "ftp" disables auto-logon.
# Note that "bell" rings 'bell' after each file transfer.

exit 0

Example A-5. copy-cd: Copying a data CD

#!/bin/bash
# copy-cd.sh: copying a data CD

CDROM=/dev/cdrom                           # CD ROM device
OF=/home/bozo/projects/cdimage.iso         # output file
#       /xxxx/xxxxxxxx/                      Change to suit your system.
BLOCKSIZE=2048
SPEED=10                                   # May use higher speed ...
DEVICE=/dev/cdrom
# DEVICE="0,0"    on older versions of cdrecord.

echo; echo "Insert source CD, but do *not* mount it."
echo "Press ENTER when ready. "
read ready                                 # Wait for input, $ready not used.

echo; echo "Copying the source CD to $OF."
echo "This may take a while. Please be patient."

dd if=$CDROM of=$OF bs=$BLOCKSIZE          # Raw device copy.


echo; echo "Remove data CD."
echo "Insert blank CDR."
echo "Press ENTER when ready. "
read ready                                 # Wait for input, $ready not used.

echo "Copying $OF to CDR."

cdrecord -v -isosize speed=$SPEED dev=$DEVICE $OF
# Uses Joerg Schilling's "cdrecord" package (see its docs).
# http://www.fokus.gmd.de/nthp/employees/schilling/cdrecord.html
# Newer Linux distros may use "wodim" rather than "cdrecord" ...


echo; echo "Done copying $OF to CDR on device $CDROM."

echo "Do you want to erase the image file (y/n)? "  # Probably a huge file.
read answer

case "$answer" in
[yY]) rm -f $OF
      echo "$OF erased."
      ;;
*)    echo "$OF not erased.";;
esac

echo

# Exercise:
# Change the above "case" statement to also accept "yes" and "Yes" as input.

exit 0

Example A-6. Collatz series

#!/bin/bash
# collatz.sh

#  The notorious "hailstone" or Collatz series.
#  -------------------------------------------
#  1) Get the integer "seed" from the command-line.
#  2) NUMBER <-- seed
#  3) Print NUMBER.
#  4)  If NUMBER is even, divide by 2, or
#  5)+ if odd, multiply by 3 and add 1.
#  6) NUMBER <-- result 
#  7) Loop back to step 3 (for specified number of iterations).
#
#  The theory is that every sequence,
#+ no matter how large the initial value,
#+ eventually settles down to repeating "4,2,1..." cycles,
#+ even after fluctuating through a wide range of values.
#
#  This is an instance of an "iterate,"
#+ an operation that feeds its output back into its input.
#  Sometimes the result is a "chaotic" series.


MAX_ITERATIONS=200
# For large seed numbers (>32000), try increasing MAX_ITERATIONS.

h=${1:-$$}                      #  Seed.
                                #  Use $PID as seed,
                                #+ if not specified as command-line arg.

echo
echo "C($h) --- $MAX_ITERATIONS Iterations"
echo

for ((i=1; i<=MAX_ITERATIONS; i++))
do

# echo -n "$h	"
#            ^^^ 
#            tab
# printf does it better ...
COLWIDTH=%7d
printf $COLWIDTH $h

  let "remainder = h % 2"
  if [ "$remainder" -eq 0 ]   # Even?
  then
    let "h /= 2"              # Divide by 2.
  else
    let "h = h*3 + 1"         # Multiply by 3 and add 1.
  fi


COLUMNS=10                    # Output 10 values per line.
let "line_break = i % $COLUMNS"
if [ "$line_break" -eq 0 ]
then
  echo
fi  

done

echo

#  For more information on this strange mathematical function,
#+ see _Computers, Pattern, Chaos, and Beauty_, by Pickover, p. 185 ff.,
#+ as listed in the bibliography.

exit 0

Example A-7. days-between: Days between two dates

#!/bin/bash
# days-between.sh:    Number of days between two dates.
# Usage: ./days-between.sh [M]M/[D]D/YYYY [M]M/[D]D/YYYY
#
# Note: Script modified to account for changes in Bash, v. 2.05b +,
#+      that closed the loophole permitting large negative
#+      integer return values.

ARGS=2                # Two command-line parameters expected.
E_PARAM_ERR=85        # Param error.

REFYR=1600            # Reference year.
CENTURY=100
DIY=365
ADJ_DIY=367           # Adjusted for leap year + fraction.
MIY=12
DIM=31
LEAPCYCLE=4

MAXRETVAL=255         #  Largest permissible
                      #+ positive return value from a function.

diff=                 # Declare global variable for date difference.
value=                # Declare global variable for absolute value.
day=                  # Declare globals for day, month, year.
month=
year=


Param_Error ()        # Command-line parameters wrong.
{
  echo "Usage: `basename $0` [M]M/[D]D/YYYY [M]M/[D]D/YYYY"
  echo "       (date must be after 1/3/1600)"
  exit $E_PARAM_ERR
}  


Parse_Date ()                 # Parse date from command-line params.
{
  month=${1%%/**}
  dm=${1%/**}                 # Day and month.
  day=${dm#*/}
  let "year = `basename $1`"  # Not a filename, but works just the same.
}  


check_date ()                 # Checks for invalid date(s) passed.
{
  [ "$day" -gt "$DIM" ] || [ "$month" -gt "$MIY" ] ||
  [ "$year" -lt "$REFYR" ] && Param_Error
  # Exit script on bad value(s).
  # Uses or-list / and-list.
  #
  # Exercise: Implement more rigorous date checking.
}


strip_leading_zero () #  Better to strip possible leading zero(s)
{                     #+ from day and/or month
  return ${1#0}       #+ since otherwise Bash will interpret them
}                     #+ as octal values (POSIX.2, sect 2.9.2.1).


day_index ()          # Gauss' Formula:
{                     # Days from March 1, 1600 to date passed as param.
                      #           ^^^^^^^^^^^^^
  day=$1
  month=$2
  year=$3

  let "month = $month - 2"
  if [ "$month" -le 0 ]
  then
    let "month += 12"
    let "year -= 1"
  fi  

  let "year -= $REFYR"
  let "indexyr = $year / $CENTURY"


  let "Days = $DIY*$year + $year/$LEAPCYCLE - $indexyr \
              + $indexyr/$LEAPCYCLE + $ADJ_DIY*$month/$MIY + $day - $DIM"
  #  For an in-depth explanation of this algorithm, see
  #+   http://weblogs.asp.net/pgreborio/archive/2005/01/06/347968.aspx


  echo $Days

}  


calculate_difference ()            # Difference between two day indices.
{
  let "diff = $1 - $2"             # Global variable.
}  


abs ()                             #  Absolute value
{                                  #  Uses global "value" variable.
  if [ "$1" -lt 0 ]                #  If negative
  then                             #+ then
    let "value = 0 - $1"           #+ change sign,
  else                             #+ else
    let "value = $1"               #+ leave it alone.
  fi
}



if [ $# -ne "$ARGS" ]              # Require two command-line params.
then
  Param_Error
fi  

Parse_Date $1
check_date $day $month $year       #  See if valid date.

strip_leading_zero $day            #  Remove any leading zeroes
day=$?                             #+ on day and/or month.
strip_leading_zero $month
month=$?

let "date1 = `day_index $day $month $year`"


Parse_Date $2
check_date $day $month $year

strip_leading_zero $day
day=$?
strip_leading_zero $month
month=$?

date2=$(day_index $day $month $year) # Command substitution.


calculate_difference $date1 $date2

abs $diff                            # Make sure it's positive.
diff=$value

echo $diff

exit 0

#  Exercise:
#  --------
#  If given only one command-line parameter, have the script
#+ use today's date as the second.


#  Compare this script with
#+ the implementation of Gauss' Formula in a C program at
#+    http://buschencrew.hypermart.net/software/datedif

Example A-8. Making a dictionary

#!/bin/bash
# makedict.sh  [make dictionary]

# Modification of /usr/sbin/mkdict (/usr/sbin/cracklib-forman) script.
# Original script copyright 1993, by Alec Muffett.
#
#  This modified script included in this document in a manner
#+ consistent with the "LICENSE" document of the "Crack" package
#+ that the original script is a part of.

#  This script processes text files to produce a sorted list
#+ of words found in the files.
#  This may be useful for compiling dictionaries
#+ and for other lexicographic purposes.


E_BADARGS=65

if [ ! -r "$1" ]                    #  Need at least one
then                                #+ valid file argument.
  echo "Usage: $0 files-to-process"
  exit $E_BADARGS
fi  


# SORT="sort"                       #  No longer necessary to define options
                                    #+ to sort. Changed from original script.

cat $* |                            # Contents of specified files to stdout.
        tr A-Z a-z |                # Convert to lowercase.
        tr ' ' '\012' |             # New: change spaces to newlines.
#       tr -cd '\012[a-z][0-9]' |   #  Get rid of everything non-alphanumeric
                                    #+ (in original script).
        tr -c '\012a-z'  '\012' |   #  Rather than deleting non-alpha chars,
                                    #+ change them to newlines.
        sort |                      # $SORT options unnecessary now.
        uniq |                      # Remove duplicates.
        grep -v '^#' |              # Delete lines beginning with a hashmark.
        grep -v '^$'                # Delete blank lines.

exit 0

Example A-9. Soundex conversion

#!/bin/bash
# soundex.sh: Calculate "soundex" code for names

# =======================================================
#        Soundex script
#              by
#         Mendel Cooper
#     thegrendel.abs@gmail.com
#     reldate: 23 January, 2002
#
#   Placed in the Public Domain.
#
# A slightly different version of this script appeared in
#+ Ed Schaefer's July, 2002 "Shell Corner" column
#+ in "Unix Review" on-line,
#+ http://www.unixreview.com/documents/uni1026336632258/
# =======================================================


ARGCOUNT=1                     # Need name as argument.
E_WRONGARGS=90

if [ $# -ne "$ARGCOUNT" ]
then
  echo "Usage: `basename $0` name"
  exit $E_WRONGARGS
fi  


assign_value ()                #  Assigns numerical value
{                              #+ to letters of name.

  val1=bfpv                    # 'b,f,p,v' = 1
  val2=cgjkqsxz                # 'c,g,j,k,q,s,x,z' = 2
  val3=dt                      #  etc.
  val4=l
  val5=mn
  val6=r

# Exceptionally clever use of 'tr' follows.
# Try to figure out what is going on here.

value=$( echo "$1" \
| tr -d wh \
| tr $val1 1 | tr $val2 2 | tr $val3 3 \
| tr $val4 4 | tr $val5 5 | tr $val6 6 \
| tr -s 123456 \
| tr -d aeiouy )

# Assign letter values.
# Remove duplicate numbers, except when separated by vowels.
# Ignore vowels, except as separators, so delete them last.
# Ignore 'w' and 'h', even as separators, so delete them first.
#
# The above command substitution lays more pipe than a plumber <g>.

}  


input_name="$1"
echo
echo "Name = $input_name"


# Change all characters of name input to lowercase.
# ------------------------------------------------
name=$( echo $input_name | tr A-Z a-z )
# ------------------------------------------------
# Just in case argument to script is mixed case.


# Prefix of soundex code: first letter of name.
# --------------------------------------------


char_pos=0                     # Initialize character position. 
prefix0=${name:$char_pos:1}
prefix=`echo $prefix0 | tr a-z A-Z`
                               # Uppercase 1st letter of soundex.

let "char_pos += 1"            # Bump character position to 2nd letter of name.
name1=${name:$char_pos}


# ++++++++++++++++++++++++++ Exception Patch ++++++++++++++++++++++++++++++
#  Now, we run both the input name and the name shifted one char
#+ to the right through the value-assigning function.
#  If we get the same value out, that means that the first two characters
#+ of the name have the same value assigned, and that one should cancel.
#  However, we also need to test whether the first letter of the name
#+ is a vowel or 'w' or 'h', because otherwise this would bollix things up.

char1=`echo $prefix | tr A-Z a-z`    # First letter of name, lowercased.

assign_value $name
s1=$value
assign_value $name1
s2=$value
assign_value $char1
s3=$value
s3=9$s3                              #  If first letter of name is a vowel
                                     #+ or 'w' or 'h',
                                     #+ then its "value" will be null (unset).
				     #+ Therefore, set it to 9, an otherwise
				     #+ unused value, which can be tested for.


if [[ "$s1" -ne "$s2" || "$s3" -eq 9 ]]
then
  suffix=$s2
else  
  suffix=${s2:$char_pos}
fi  
# ++++++++++++++++++++++ end Exception Patch ++++++++++++++++++++++++++++++


padding=000                    # Use at most 3 zeroes to pad.


soun=$prefix$suffix$padding    # Pad with zeroes.

MAXLEN=4                       # Truncate to maximum of 4 chars.
soundex=${soun:0:$MAXLEN}

echo "Soundex = $soundex"

echo

#  The soundex code is a method of indexing and classifying names
#+ by grouping together the ones that sound alike.
#  The soundex code for a given name is the first letter of the name,
#+ followed by a calculated three-number code.
#  Similar sounding names should have almost the same soundex codes.

#   Examples:
#   Smith and Smythe both have a "S-530" soundex.
#   Harrison = H-625
#   Hargison = H-622
#   Harriman = H-655

#  This works out fairly well in practice, but there are numerous anomalies.
#
#
#  The U.S. Census and certain other governmental agencies use soundex,
#  as do genealogical researchers.
#
#  For more information,
#+ see the "National Archives and Records Administration home page",
#+ http://www.nara.gov/genealogy/soundex/soundex.html



# Exercise:
# --------
# Simplify the "Exception Patch" section of this script.

exit 0

Example A-10. Game of Life

#!/bin/bash
# life.sh: "Life in the Slow Lane"

# Version 0.2:   Patched by Daniel Albers
#+               to allow non-square grids as input.
# Version 0.2.1: Added 2-second delay between generations.

# ##################################################################### #
# This is the Bash script version of John Conway's "Game of Life".      #
# "Life" is a simple implementation of cellular automata.               #
# --------------------------------------------------------------------- #
# On a rectangular grid, let each "cell" be either "living" or "dead."  #
# Designate a living cell with a dot, and a dead one with a blank space.#
#  Begin with an arbitrarily drawn dot-and-blank grid,                  #
#+ and let this be the starting generation, "generation 0."             #
# Determine each successive generation by the following rules:          #
#   1) Each cell has 8 neighbors, the adjoining cells                   #
#+     left, right, top, bottom, and the 4 diagonals.                   #
#                                                                       #
#                       123                                             #
#                       4*5     The * is the cell under consideration.  #
#                       678                                             #
#                                                                       #
# 2) A living cell with either 2 or 3 living neighbors remains alive.   #
SURVIVE=2                                                               #
# 3) A dead cell with 3 living neighbors comes alive (a "birth").       #
BIRTH=3                                                                 #
# 4) All other cases result in a dead cell for the next generation.     #
# ##################################################################### #


startfile=gen0   # Read the starting generation from the file "gen0" ...
                 # Default, if no other file specified when invoking script.
                 #
if [ -n "$1" ]   # Specify another "generation 0" file.
then
    startfile="$1"
fi  

############################################
#  Abort script if "startfile" not specified
#+ and
#+ default file "gen0" not present.

E_NOSTARTFILE=86

if [ ! -e "$startfile" ]
then
  echo "Startfile \""$startfile"\" missing!"
  exit $E_NOSTARTFILE
fi
############################################


ALIVE1=.
DEAD1=_
                 # Represent living and dead cells in the start-up file.

#  ---------------------------------------------------------- #
#  This script uses a 10 x 10 grid (may be increased,
#+ but a large grid will slow execution).
ROWS=10
COLS=10
#  Change above two variables to match grid size, as desired.
#  ---------------------------------------------------------- #

GENERATIONS=10          #  How many generations to cycle through.
                        #  Adjust this upwards
                        #+ if you have time on your hands.

NONE_ALIVE=85           #  Exit status on premature bailout,
                        #+ if no cells left alive.
DELAY=2                 #  Pause between generations, etc.
TRUE=0
FALSE=1
ALIVE=0
DEAD=1

avar=                   # Global; holds current generation.
generation=0            # Initialize generation count.

# =================================================================

let "cells = $ROWS * $COLS"   # How many cells.

# Arrays containing "cells."
declare -a initial
declare -a current

display ()
{

alive=0                 # How many cells alive at any given time.
                        # Initially zero.

declare -a arr
arr=( `echo "$1"` )     # Convert passed arg to array.

element_count=${#arr[*]}

local i
local rowcheck

for ((i=0; i<$element_count; i++))
do

  # Insert newline at end of each row.
  let "rowcheck = $i % COLS"
  if [ "$rowcheck" -eq 0 ]
  then
    echo                # Newline.
    echo -n "      "    # Indent.
  fi  

  cell=${arr[i]}

  if [ "$cell" = . ]
  then
    let "alive += 1"
  fi  

  echo -n "$cell" | sed -e 's/_/ /g'
  # Print out array, changing underscores to spaces.
done  

return

}

IsValid ()                            # Test whether cell coordinate valid.
{

  if [ -z "$1"  -o -z "$2" ]          # Mandatory arguments missing?
  then
    return $FALSE
  fi

local row
local lower_limit=0                   # Disallow negative coordinate.
local upper_limit
local left
local right

let "upper_limit = $ROWS * $COLS - 1" # Total number of cells.


if [ "$1" -lt "$lower_limit" -o "$1" -gt "$upper_limit" ]
then
  return $FALSE                       # Out of array bounds.
fi  

row=$2
let "left = $row * $COLS"             # Left limit.
let "right = $left + $COLS - 1"       # Right limit.

if [ "$1" -lt "$left" -o "$1" -gt "$right" ]
then
  return $FALSE                       # Beyond row boundary.
fi  

return $TRUE                          # Valid coordinate.

}  


IsAlive ()              #  Test whether cell is alive.
                        #  Takes array, cell number, and
{                       #+ state of cell as arguments.
  GetCount "$1" $2      #  Get alive cell count in neighborhood.
  local nhbd=$?

  if [ "$nhbd" -eq "$BIRTH" ]  # Alive in any case.
  then
    return $ALIVE
  fi

  if [ "$3" = "." -a "$nhbd" -eq "$SURVIVE" ]
  then                  # Alive only if previously alive.
    return $ALIVE
  fi  

  return $DEAD          # Dead, by default.

}  


GetCount ()             # Count live cells in passed cell's neighborhood.
                        # Two arguments needed:
			# $1) variable holding array
			# $2) cell number
{
  local cell_number=$2
  local array
  local top
  local center
  local bottom
  local r
  local row
  local i
  local t_top
  local t_cen
  local t_bot
  local count=0
  local ROW_NHBD=3

  array=( `echo "$1"` )

  let "top = $cell_number - $COLS - 1"    # Set up cell neighborhood.
  let "center = $cell_number - 1"
  let "bottom = $cell_number + $COLS - 1"
  let "r = $cell_number / $COLS"

  for ((i=0; i<$ROW_NHBD; i++))           # Traverse from left to right. 
  do
    let "t_top = $top + $i"
    let "t_cen = $center + $i"
    let "t_bot = $bottom + $i"


    let "row = $r"                        # Count center row.
    IsValid $t_cen $row                   # Valid cell position?
    if [ $? -eq "$TRUE" ]
    then
      if [ ${array[$t_cen]} = "$ALIVE1" ] # Is it alive?
      then                                # If yes, then ...
        let "count += 1"                  # Increment count.
      fi	
    fi  

    let "row = $r - 1"                    # Count top row.          
    IsValid $t_top $row
    if [ $? -eq "$TRUE" ]
    then
      if [ ${array[$t_top]} = "$ALIVE1" ] # Redundancy here.
      then                                # Can be optimized?
        let "count += 1"
      fi	
    fi  

    let "row = $r + 1"                    # Count bottom row.
    IsValid $t_bot $row
    if [ $? -eq "$TRUE" ]
    then
      if [ ${array[$t_bot]} = "$ALIVE1" ] 
      then
        let "count += 1"
      fi	
    fi  

  done  


  if [ ${array[$cell_number]} = "$ALIVE1" ]
  then
    let "count -= 1"        #  Make sure value of tested cell itself
  fi                        #+ is not counted.


  return $count
  
}

next_gen ()               # Update generation array.
{

local array
local i=0

array=( `echo "$1"` )     # Convert passed arg to array.

while [ "$i" -lt "$cells" ]
do
  IsAlive "$1" $i ${array[$i]}   # Is cell alive?
  if [ $? -eq "$ALIVE" ]
  then                           #  If alive, then
    array[$i]=.                  #+ represent the cell as a period.
  else  
    array[$i]="_"                #  Otherwise underscore
   fi                            #+ (will later be converted to space).
  let "i += 1" 
done   


# let "generation += 1"          # Increment generation count.
# Why was the above line commented out?


# Set variable to pass as parameter to "display" function.
avar=`echo ${array[@]}`   # Convert array back to string variable.
display "$avar"           # Display it.
echo; echo
echo "Generation $generation  -  $alive alive"

if [ "$alive" -eq 0 ]
then
  echo
  echo "Premature exit: no more cells alive!"
  exit $NONE_ALIVE        #  No point in continuing
fi                        #+ if no live cells.

}


# =========================================================

# main ()

# Load initial array with contents of startup file.
initial=( `cat "$startfile" | sed -e '/#/d' | tr -d '\n' |\
# Delete lines containing '#' comment character.
           sed -e 's/\./\. /g' -e 's/_/_ /g'` )
# Remove linefeeds and insert space between elements.

clear          # Clear screen.

echo #         Title
setterm -reverse on
echo "======================="
setterm -reverse off
echo "    $GENERATIONS generations"
echo "           of"
echo "\"Life in the Slow Lane\""
setterm -reverse on
echo "======================="
setterm -reverse off

sleep $DELAY   # Display "splash screen" for 2 seconds.


# -------- Display first generation. --------
Gen0=`echo ${initial[@]}`
display "$Gen0"           # Display only.
echo; echo
echo "Generation $generation  -  $alive alive"
sleep $DELAY
# -------------------------------------------


let "generation += 1"     # Bump generation count.
echo

# ------- Display second generation. -------
Cur=`echo ${initial[@]}`
next_gen "$Cur"          # Update & display.
sleep $DELAY
# ------------------------------------------

let "generation += 1"     # Increment generation count.

# ------ Main loop for displaying subsequent generations ------
while [ "$generation" -le "$GENERATIONS" ]
do
  Cur="$avar"
  next_gen "$Cur"
  let "generation += 1"
  sleep $DELAY
done
# ==============================================================

echo

exit 0   # CEOF:EOF



# The grid in this script has a "boundary problem."
# The the top, bottom, and sides border on a void of dead cells.
# Exercise: Change the script to have the grid wrap around,
# +         so that the left and right sides will "touch,"      
# +         as will the top and bottom.
#
# Exercise: Create a new "gen0" file to seed this script.
#           Use a 12 x 16 grid, instead of the original 10 x 10 one.
#           Make the necessary changes to the script,
#+          so it will run with the altered file.
#
# Exercise: Modify this script so that it can determine the grid size
#+          from the "gen0" file, and set any variables necessary
#+          for the script to run.
#           This would make unnecessary any changes to variables
#+          in the script for an altered grid size.
#
# Exercise: Optimize this script.
#           It has some redundant code.

Example A-11. Data file for Game of Life

# gen0
#
# This is an example "generation 0" start-up file for "life.sh".
# --------------------------------------------------------------
#  The "gen0" file is a 10 x 10 grid using a period (.) for live cells,
#+ and an underscore (_) for dead ones. We cannot simply use spaces
#+ for dead cells in this file because of a peculiarity in Bash arrays.
#  [Exercise for the reader: explain this.]
#
# Lines beginning with a '#' are comments, and the script ignores them.
__.__..___
___._.____
____.___..
_._______.
____._____
..__...___
____._____
___...____
__.._..___
_..___..__

+++

The following two scripts are by Mark Moraes of the University of Toronto. See the file Moraes-COPYRIGHT for permissions and restrictions. This file is included in the combined HTML/source tarball of the ABS Guide.

Example A-12. behead: Removing mail and news message headers

#! /bin/sh
# Strips off the header from a mail/News message i.e. till the first
# empty line.
# Author: Mark Moraes, University of Toronto
# See the included file "Moraes-COPYRIGHT" for copyright info.

# ==> These comments added by author of this document.

if [ $# -eq 0 ]; then
# ==> If no command-line args present, then works on file redirected to stdin.
	sed -e '1,/^$/d' -e '/^[ 	]*$/d'
	# --> Delete empty lines and all lines until 
	# --> first one beginning with white space.
else
# ==> If command-line args present, then work on files named.
	for i do
		sed -e '1,/^$/d' -e '/^[ 	]*$/d' $i
		# --> Ditto, as above.
	done
fi

# ==> Exercise: Add error checking and other options.
# ==>
# ==> Note that the small sed script repeats, except for the arg passed.
# ==> Does it make sense to embed it in a function? Why or why not?

Example A-13. ftpget: Downloading files via ftp

#! /bin/sh 
# $Id: ftpget,v 1.2 91/05/07 21:15:43 moraes Exp $ 
# Script to perform batch anonymous ftp. Essentially converts a list of
# of command-line arguments into input to ftp.
# ==> This script is nothing but a shell wrapper around "ftp" . . .
# Simple, and quick - written as a companion to ftplist 
# -h specifies the remote host (default prep.ai.mit.edu) 
# -d specifies the remote directory to cd to - you can provide a sequence 
# of -d options - they will be cd'ed to in turn. If the paths are relative, 
# make sure you get the sequence right. Be careful with relative paths - 
# there are far too many symlinks nowadays.  
# (default is the ftp login directory)
# -v turns on the verbose option of ftp, and shows all responses from the 
# ftp server.  
# -f remotefile[:localfile] gets the remote file into localfile 
# -m pattern does an mget with the specified pattern. Remember to quote 
# shell characters.  
# -c does a local cd to the specified directory
# For example, 
# 	ftpget -h expo.lcs.mit.edu -d contrib -f xplaces.shar:xplaces.sh \
#		-d ../pub/R3/fixes -c ~/fixes -m 'fix*' 
# will get xplaces.shar from ~ftp/contrib on expo.lcs.mit.edu, and put it
# in xplaces.sh in the current working directory, and get all fixes from
# ~ftp/pub/R3/fixes and put them in the ~/fixes directory. 
# Obviously, the sequence of the options is important, since the equivalent
# commands are executed by ftp in corresponding order
#
# Mark Moraes <moraes@csri.toronto.edu>, Feb 1, 1989 
#


# ==> These comments added by author of this document.

# PATH=/local/bin:/usr/ucb:/usr/bin:/bin
# export PATH
# ==> Above 2 lines from original script probably superfluous.

E_BADARGS=65

TMPFILE=/tmp/ftp.$$
# ==> Creates temp file, using process id of script ($$)
# ==> to construct filename.

SITE=`domainname`.toronto.edu
# ==> 'domainname' similar to 'hostname'
# ==> May rewrite this to parameterize this for general use.

usage="Usage: $0 [-h remotehost] [-d remotedirectory]... \ 
[-f remfile:localfile]...  [-c localdirectory] [-m filepattern] [-v]"
ftpflags="-i -n"
verbflag=
set -f 		# So we can use globbing in -m
set x `getopt vh:d:c:m:f: $*`
if [ $? != 0 ]; then
	echo $usage
	exit $E_BADARGS
fi
shift
trap 'rm -f ${TMPFILE} ; exit' 0   1     2              3        15
# ==>                   Signals:   HUP   INT (Ctl-C)    QUIT     TERM
# ==> Delete tempfile in case of abnormal exit from script.
echo "user anonymous ${USER-gnu}@${SITE} > ${TMPFILE}"
# ==> Added quotes (recommended in complex echoes).
echo binary >> ${TMPFILE}
for i in $*   # ==> Parse command-line args.
do
	case $i in
	-v) verbflag=-v; echo hash >> ${TMPFILE}; shift;;
	-h) remhost=$2; shift 2;;
	-d) echo cd $2 >> ${TMPFILE}; 
	    if [ x${verbflag} != x ]; then
	        echo pwd >> ${TMPFILE};
	    fi;
	    shift 2;;
	-c) echo lcd $2 >> ${TMPFILE}; shift 2;;
	-m) echo mget "$2" >> ${TMPFILE}; shift 2;;
	-f) f1=`expr "$2" : "\([^:]*\).*"`; f2=`expr "$2" : "[^:]*:\(.*\)"`;
	    echo get ${f1} ${f2} >> ${TMPFILE}; shift 2;;
	--) shift; break;;
	esac
        # ==> 'lcd' and 'mget' are ftp commands. See "man ftp" . . .
done
if [ $# -ne 0 ]; then
	echo $usage
	exit $E_BADARGS
        # ==> Changed from "exit 2" to conform with style standard.
fi
if [ x${verbflag} != x ]; then
	ftpflags="${ftpflags} -v"
fi
if [ x${remhost} = x ]; then
	remhost=prep.ai.mit.edu
	# ==> Change to match appropriate ftp site.
fi
echo quit >> ${TMPFILE}
# ==> All commands saved in tempfile.

ftp ${ftpflags} ${remhost} < ${TMPFILE}
# ==> Now, tempfile batch processed by ftp.

rm -f ${TMPFILE}
# ==> Finally, tempfile deleted (you may wish to copy it to a logfile).


# ==> Exercises:
# ==> ---------
# ==> 1) Add error checking.
# ==> 2) Add bells & whistles.

#  See the included file "Moraes-COPYRIGHT" for copyright info.
#+ on this script.

+

Antek Sawicki contributed the following script, which makes very clever use of the parameter substitution operators discussed in Section 9.3.

Example A-14. password: Generating random 8-character passwords

#!/bin/bash
# May need to be invoked with  #!/bin/bash2  on older machines.
#
#  Random password generator for Bash 2.x +
#+ by Antek Sawicki <tenox@tenox.tc>,
#+ who generously gave usage permission to the ABS Guide author.
#
# ==> Comments added by document author ==>


MATRIX="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
# ==> Password will consist of alphanumeric characters.
LENGTH="8"
# ==> May change 'LENGTH' for longer password.


while [ "${n:=1}" -le "$LENGTH" ]
# ==> Recall that := is "default substitution" operator.
# ==> So, if 'n' has not been initialized, set it to 1.
do
	PASS="$PASS${MATRIX:$(($RANDOM%${#MATRIX})):1}"
	# ==> Very clever, but tricky.

	# ==> Starting from the innermost nesting...
	# ==> ${#MATRIX} returns length of array MATRIX.

	# ==> $RANDOM%${#MATRIX} returns random number between 1
	# ==> and [length of MATRIX] - 1.

	# ==> ${MATRIX:$(($RANDOM%${#MATRIX})):1}
	# ==> returns expansion of MATRIX at random position, by length 1. 
	# ==> See {var:pos:len} parameter substitution in Chapter 9.
	# ==> and the associated examples.

	# ==> PASS=... simply pastes this result onto previous PASS (concatenation).

	# ==> To visualize this more clearly, uncomment the following line
	#                 echo "$PASS"
	# ==> to see PASS being built up,
	# ==> one character at a time, each iteration of the loop.

	let n+=1
	# ==> Increment 'n' for next pass.
done

echo "$PASS"      # ==> Or, redirect to a file, as desired.

exit 0

+

James R. Van Zandt contributed this script which uses named pipes and, in his words, "really exercises quoting and escaping."

Example A-15. fifo: Making daily backups, using named pipes

#!/bin/bash
# ==> Script by James R. Van Zandt, and used here with his permission.

# ==> Comments added by author of this document.

  
  HERE=`uname -n`    # ==> hostname
  THERE=bilbo
  echo "starting remote backup to $THERE at `date +%r`"
  # ==> `date +%r` returns time in 12-hour format, i.e. "08:08:34 PM".
  
  # make sure /pipe really is a pipe and not a plain file
  rm -rf /pipe
  mkfifo /pipe       # ==> Create a "named pipe", named "/pipe" ...
  
  # ==> 'su xyz' runs commands as user "xyz".
  # ==> 'ssh' invokes secure shell (remote login client).
  su xyz -c "ssh $THERE \"cat > /home/xyz/backup/${HERE}-daily.tar.gz\" < /pipe"&
  cd /
  tar -czf - bin boot dev etc home info lib man root sbin share usr var > /pipe
  # ==> Uses named pipe, /pipe, to communicate between processes:
  # ==> 'tar/gzip' writes to /pipe and 'ssh' reads from /pipe.

  # ==> The end result is this backs up the main directories, from / on down.

  # ==>  What are the advantages of a "named pipe" in this situation,
  # ==>+ as opposed to an "anonymous pipe", with |?
  # ==>  Will an anonymous pipe even work here?

  # ==>  Is it necessary to delete the pipe before exiting the script?
  # ==>  How could that be done?


  exit 0

+

StИphane Chazelas used the following script to demonstrate generating prime numbers without arrays.

Example A-16. Generating prime numbers using the modulo operator

#!/bin/bash
# primes.sh: Generate prime numbers, without using arrays.
# Script contributed by Stephane Chazelas.

#  This does *not* use the classic "Sieve of Eratosthenes" algorithm,
#+ but instead the more intuitive method of testing each candidate number
#+ for factors (divisors), using the "%" modulo operator.


LIMIT=1000                    # Primes, 2 ... 1000.

Primes()
{
 (( n = $1 + 1 ))             # Bump to next integer.
 shift                        # Next parameter in list.
#  echo "_n=$n i=$i_"
 
 if (( n == LIMIT ))
 then echo $*
 return
 fi

 for i; do                    # "i" set to "@", previous values of $n.
#   echo "-n=$n i=$i-"
   (( i * i > n )) && break   # Optimization.
   (( n % i )) && continue    # Sift out non-primes using modulo operator.
   Primes $n $@               # Recursion inside loop.
   return
   done

   Primes $n $@ $n            #  Recursion outside loop.
                              #  Successively accumulate
			      #+ positional parameters.
                              #  "$@" is the accumulating list of primes.
}

Primes 1

exit $?

# Pipe output of the script to 'fmt' for prettier printing.

#  Uncomment lines 16 and 24 to help figure out what is going on.

#  Compare the speed of this algorithm for generating primes
#+ with the Sieve of Eratosthenes (ex68.sh).


#  Exercise: Rewrite this script without recursion.

+

Rick Boivie's revision of Jordi Sanfeliu's tree script.

Example A-17. tree: Displaying a directory tree

#!/bin/bash
# tree.sh

#  Written by Rick Boivie.
#  Used with permission.
#  This is a revised and simplified version of a script
#+ by Jordi Sanfeliu (the original author), and patched by Ian Kjos.
#  This script replaces the earlier version used in
#+ previous releases of the Advanced Bash Scripting Guide.
#  Copyright (c) 2002, by Jordi Sanfeliu, Rick Boivie, and Ian Kjos.

# ==> Comments added by the author of this document.


search () {
for dir in `echo *`
#  ==> `echo *` lists all the files in current working directory,
#+ ==> without line breaks.
#  ==> Similar effect to for dir in *
#  ==> but "dir in `echo *`" will not handle filenames with blanks.
do
  if [ -d "$dir" ] ; then # ==> If it is a directory (-d)...
  zz=0                    # ==> Temp variable, keeping track of
                          #     directory level.
  while [ $zz != $1 ]     # Keep track of inner nested loop.
    do
      echo -n "| "        # ==> Display vertical connector symbol,
                          # ==> with 2 spaces & no line feed
                          #     in order to indent.
      zz=`expr $zz + 1`   # ==> Increment zz.
    done

    if [ -L "$dir" ] ; then # ==> If directory is a symbolic link...
      echo "+---$dir" `ls -l $dir | sed 's/^.*'$dir' //'`
      # ==> Display horiz. connector and list directory name, but...
      # ==> delete date/time part of long listing.
    else
      echo "+---$dir"       # ==> Display horizontal connector symbol...
      # ==> and print directory name.
      numdirs=`expr $numdirs + 1` # ==> Increment directory count.
      if cd "$dir" ; then         # ==> If can move to subdirectory...
        search `expr $1 + 1`      # with recursion ;-)
        # ==> Function calls itself.
        cd ..
      fi
    fi
  fi
done
}

if [ $# != 0 ] ; then
  cd $1   # Move to indicated directory.
  #else   # stay in current directory
fi

echo "Initial directory = `pwd`"
numdirs=0

search 0
echo "Total directories = $numdirs"

exit 0

Patsie's version of a directory tree script.

Example A-18. tree2: Alternate directory tree script

#!/bin/bash
# tree2.sh

# Lightly modified/reformatted by ABS Guide author.
# Included in ABS Guide with permission of script author (thanks!).

## Recursive file/dirsize checking script, by Patsie
##
## This script builds a list of files/directories and their size (du -akx)
## and processes this list to a human readable tree shape
## The 'du -akx' is only as good as the permissions the owner has.
## So preferably run as root* to get the best results, or use only on
## directories for which you have read permissions. Anything you can't
## read is not in the list.

#* ABS Guide author advises caution when running scripts as root!


##########  THIS IS CONFIGURABLE  ##########

TOP=5                   # Top 5 biggest (sub)directories.
MAXRECURS=5             # Max 5 subdirectories/recursions deep.
E_BL=80                 # Blank line already returned.
E_DIR=81                # Directory not specified.


##########  DON'T CHANGE ANYTHING BELOW THIS LINE  ##########

PID=$$                            # Our own process ID.
SELF=`basename $0`                # Our own program name.
TMP="/tmp/${SELF}.${PID}.tmp"     # Temporary 'du' result.

# Convert number to dotted thousand.
function dot { echo "            $*" |
               sed -e :a -e 's/\(.*[0-9]\)\([0-9]\{3\}\)/\1,\2/;ta' |
               tail -c 12; }

# Usage: tree <recursion> <indent prefix> <min size> <directory>
function tree {
  recurs="$1"           # How deep nested are we?
  prefix="$2"           # What do we display before file/dirname?
  minsize="$3"          # What is the minumum file/dirsize?
  dirname="$4"          # Which directory are we checking?

# Get ($TOP) biggest subdirs/subfiles from TMP file.
  LIST=`egrep "[[:space:]]${dirname}/[^/]*$" "$TMP" |
        awk '{if($1>'$minsize') print;}' | sort -nr | head -$TOP`
  [ -z "$LIST" ] && return        # Empty list, then go back.

  cnt=0
  num=`echo "$LIST" | wc -l`      # How many entries in the list.

  ## Main loop
  echo "$LIST" | while read size name; do
    ((cnt+=1))		          # Count entry number.
    bname=`basename "$name"`      # We only need a basename of the entry.
    [ -d "$name" ] && bname="$bname/"
                                  # If it's a directory, append a slash.
    echo "`dot $size`$prefix +-$bname"
                                  # Display the result.
    #  Call ourself recursively if it's a directory
    #+ and we're not nested too deep ($MAXRECURS).
    #  The recursion goes up: $((recurs+1))
    #  The prefix gets a space if it's the last entry,
    #+ or a pipe if there are more entries.
    #  The minimum file/dirsize becomes
    #+ a tenth of his parent: $((size/10)).
    # Last argument is the full directory name to check.
    if [ -d "$name" -a $recurs -lt $MAXRECURS ]; then
      [ $cnt -lt $num ] \
        || (tree $((recurs+1)) "$prefix  " $((size/10)) "$name") \
        && (tree $((recurs+1)) "$prefix |" $((size/10)) "$name")
    fi
  done

  [ $? -eq 0 ] && echo "           $prefix"
  # Every time we jump back add a 'blank' line.
  return $E_BL
  # We return 80 to tell we added a blank line already.
}

###                ###
###  main program  ###
###                ###

rootdir="$@"
[ -d "$rootdir" ] ||
  { echo "$SELF: Usage: $SELF <directory>" >&2; exit $E_DIR; }
  # We should be called with a directory name.

echo "Building inventory list, please wait ..."
     # Show "please wait" message.
du -akx "$rootdir" 1>"$TMP" 2>/dev/null
     # Build a temporary list of all files/dirs and their size.
size=`tail -1 "$TMP" | awk '{print $1}'`
     # What is our rootdirectory's size?
echo "`dot $size` $rootdir"
     # Display rootdirectory's entry.
tree 0 "" 0 "$rootdir"
     # Display the tree below our rootdirectory.

rm "$TMP" 2>/dev/null
     # Clean up TMP file.

exit $?

Noah Friedman permitted use of his string function script. It essentially reproduces some of the C-library string manipulation functions.

Example A-19. string functions: C-style string functions

#!/bin/bash

# string.bash --- bash emulation of string(3) library routines
# Author: Noah Friedman <friedman@prep.ai.mit.edu>
# ==>     Used with his kind permission in this document.
# Created: 1992-07-01
# Last modified: 1993-09-29
# Public domain

# Conversion to bash v2 syntax done by Chet Ramey

# Commentary:
# Code:

#:docstring strcat:
# Usage: strcat s1 s2
#
# Strcat appends the value of variable s2 to variable s1. 
#
# Example:
#    a="foo"
#    b="bar"
#    strcat a b
#    echo $a
#    => foobar
#
#:end docstring:

###;;;autoload   ==> Autoloading of function commented out.
function strcat ()
{
    local s1_val s2_val

    s1_val=${!1}                        # indirect variable expansion
    s2_val=${!2}
    eval "$1"=\'"${s1_val}${s2_val}"\'
    # ==> eval $1='${s1_val}${s2_val}' avoids problems,
    # ==> if one of the variables contains a single quote.
}

#:docstring strncat:
# Usage: strncat s1 s2 $n
# 
# Line strcat, but strncat appends a maximum of n characters from the value
# of variable s2.  It copies fewer if the value of variabl s2 is shorter
# than n characters.  Echoes result on stdout.
#
# Example:
#    a=foo
#    b=barbaz
#    strncat a b 3
#    echo $a
#    => foobar
#
#:end docstring:

###;;;autoload
function strncat ()
{
    local s1="$1"
    local s2="$2"
    local -i n="$3"
    local s1_val s2_val

    s1_val=${!s1}                       # ==> indirect variable expansion
    s2_val=${!s2}

    if [ ${#s2_val} -gt ${n} ]; then
       s2_val=${s2_val:0:$n}            # ==> substring extraction
    fi

    eval "$s1"=\'"${s1_val}${s2_val}"\'
    # ==> eval $1='${s1_val}${s2_val}' avoids problems,
    # ==> if one of the variables contains a single quote.
}

#:docstring strcmp:
# Usage: strcmp $s1 $s2
#
# Strcmp compares its arguments and returns an integer less than, equal to,
# or greater than zero, depending on whether string s1 is lexicographically
# less than, equal to, or greater than string s2.
#:end docstring:

###;;;autoload
function strcmp ()
{
    [ "$1" = "$2" ] && return 0

    [ "${1}" '<' "${2}" ] > /dev/null && return -1

    return 1
}

#:docstring strncmp:
# Usage: strncmp $s1 $s2 $n
# 
# Like strcmp, but makes the comparison by examining a maximum of n
# characters (n less than or equal to zero yields equality).
#:end docstring:

###;;;autoload
function strncmp ()
{
    if [ -z "${3}" -o "${3}" -le "0" ]; then
       return 0
    fi
   
    if [ ${3} -ge ${#1} -a ${3} -ge ${#2} ]; then
       strcmp "$1" "$2"
       return $?
    else
       s1=${1:0:$3}
       s2=${2:0:$3}
       strcmp $s1 $s2
       return $?
    fi
}

#:docstring strlen:
# Usage: strlen s
#
# Strlen returns the number of characters in string literal s.
#:end docstring:

###;;;autoload
function strlen ()
{
    eval echo "\${#${1}}"
    # ==> Returns the length of the value of the variable
    # ==> whose name is passed as an argument.
}

#:docstring strspn:
# Usage: strspn $s1 $s2
# 
# Strspn returns the length of the maximum initial segment of string s1,
# which consists entirely of characters from string s2.
#:end docstring:

###;;;autoload
function strspn ()
{
    # Unsetting IFS allows whitespace to be handled as normal chars. 
    local IFS=
    local result="${1%%[!${2}]*}"
 
    echo ${#result}
}

#:docstring strcspn:
# Usage: strcspn $s1 $s2
#
# Strcspn returns the length of the maximum initial segment of string s1,
# which consists entirely of characters not from string s2.
#:end docstring:

###;;;autoload
function strcspn ()
{
    # Unsetting IFS allows whitspace to be handled as normal chars. 
    local IFS=
    local result="${1%%[${2}]*}"
 
    echo ${#result}
}

#:docstring strstr:
# Usage: strstr s1 s2
# 
# Strstr echoes a substring starting at the first occurrence of string s2 in
# string s1, or nothing if s2 does not occur in the string.  If s2 points to
# a string of zero length, strstr echoes s1.
#:end docstring:

###;;;autoload
function strstr ()
{
    # if s2 points to a string of zero length, strstr echoes s1
    [ ${#2} -eq 0 ] && { echo "$1" ; return 0; }

    # strstr echoes nothing if s2 does not occur in s1
    case "$1" in
    *$2*) ;;
    *) return 1;;
    esac

    # use the pattern matching code to strip off the match and everything
    # following it
    first=${1/$2*/}

    # then strip off the first unmatched portion of the string
    echo "${1##$first}"
}

#:docstring strtok:
# Usage: strtok s1 s2
#
# Strtok considers the string s1 to consist of a sequence of zero or more
# text tokens separated by spans of one or more characters from the
# separator string s2.  The first call (with a non-empty string s1
# specified) echoes a string consisting of the first token on stdout. The
# function keeps track of its position in the string s1 between separate
# calls, so that subsequent calls made with the first argument an empty
# string will work through the string immediately following that token.  In
# this way subsequent calls will work through the string s1 until no tokens
# remain.  The separator string s2 may be different from call to call.
# When no token remains in s1, an empty value is echoed on stdout.
#:end docstring:

###;;;autoload
function strtok ()
{
 :
}

#:docstring strtrunc:
# Usage: strtrunc $n $s1 {$s2} {$...}
#
# Used by many functions like strncmp to truncate arguments for comparison.
# Echoes the first n characters of each string s1 s2 ... on stdout. 
#:end docstring:

###;;;autoload
function strtrunc ()
{
    n=$1 ; shift
    for z; do
        echo "${z:0:$n}"
    done
}

# provide string

# string.bash ends here


# ========================================================================== #
# ==> Everything below here added by the document author.

# ==> Suggested use of this script is to delete everything below here,
# ==> and "source" this file into your own scripts.

# strcat
string0=one
string1=two
echo
echo "Testing \"strcat\" function:"
echo "Original \"string0\" = $string0"
echo "\"string1\" = $string1"
strcat string0 string1
echo "New \"string0\" = $string0"
echo

# strlen
echo
echo "Testing \"strlen\" function:"
str=123456789
echo "\"str\" = $str"
echo -n "Length of \"str\" = "
strlen str
echo



# Exercise:
# --------
# Add code to test all the other string functions above.


exit 0

Michael Zick's complex array example uses the md5sum check sum command to encode directory information.

Example A-20. Directory information

#! /bin/bash
# directory-info.sh
# Parses and lists directory information.

# NOTE: Change lines 273 and 353 per "README" file.

# Michael Zick is the author of this script.
# Used here with his permission.

# Controls
# If overridden by command arguments, they must be in the order:
#   Arg1: "Descriptor Directory"
#   Arg2: "Exclude Paths"
#   Arg3: "Exclude Directories"
#
# Environment Settings override Defaults.
# Command arguments override Environment Settings.

# Default location for content addressed file descriptors.
MD5UCFS=${1:-${MD5UCFS:-'/tmpfs/ucfs'}}

# Directory paths never to list or enter
declare -a \
  EXCLUDE_PATHS=${2:-${EXCLUDE_PATHS:-'(/proc /dev /devfs /tmpfs)'}}

# Directories never to list or enter
declare -a \
  EXCLUDE_DIRS=${3:-${EXCLUDE_DIRS:-'(ucfs lost+found tmp wtmp)'}}

# Files never to list or enter
declare -a \
  EXCLUDE_FILES=${3:-${EXCLUDE_FILES:-'(core "Name with Spaces")'}}


# Here document used as a comment block.
: <<LSfieldsDoc
# # # # # List Filesystem Directory Information # # # # #
#
#	ListDirectory "FileGlob" "Field-Array-Name"
# or
#	ListDirectory -of "FileGlob" "Field-Array-Filename"
#	'-of' meaning 'output to filename'
# # # # #

String format description based on: ls (GNU fileutils) version 4.0.36

Produces a line (or more) formatted:
inode permissions hard-links owner group ...
32736 -rw-------    1 mszick   mszick

size    day month date hh:mm:ss year path
2756608 Sun Apr 20 08:53:06 2003 /home/mszick/core

Unless it is formatted:
inode permissions hard-links owner group ...
266705 crw-rw----    1    root  uucp

major minor day month date hh:mm:ss year path
4,  68 Sun Apr 20 09:27:33 2003 /dev/ttyS4
NOTE: that pesky comma after the major number

NOTE: the 'path' may be multiple fields:
/home/mszick/core
/proc/982/fd/0 -> /dev/null
/proc/982/fd/1 -> /home/mszick/.xsession-errors
/proc/982/fd/13 -> /tmp/tmpfZVVOCs (deleted)
/proc/982/fd/7 -> /tmp/kde-mszick/ksycoca
/proc/982/fd/8 -> socket:[11586]
/proc/982/fd/9 -> pipe:[11588]

If that isn't enough to keep your parser guessing,
either or both of the path components may be relative:
../Built-Shared -> Built-Static
../linux-2.4.20.tar.bz2 -> ../../../SRCS/linux-2.4.20.tar.bz2

The first character of the 11 (10?) character permissions field:
's' Socket
'd' Directory
'b' Block device
'c' Character device
'l' Symbolic link
NOTE: Hard links not marked - test for identical inode numbers
on identical filesystems.
All information about hard linked files are shared, except
for the names and the name's location in the directory system.
NOTE: A "Hard link" is known as a "File Alias" on some systems.
'-' An undistingushed file

Followed by three groups of letters for: User, Group, Others
Character 1: '-' Not readable; 'r' Readable
Character 2: '-' Not writable; 'w' Writable
Character 3, User and Group: Combined execute and special
'-' Not Executable, Not Special
'x' Executable, Not Special
's' Executable, Special
'S' Not Executable, Special
Character 3, Others: Combined execute and sticky (tacky?)
'-' Not Executable, Not Tacky
'x' Executable, Not Tacky
't' Executable, Tacky
'T' Not Executable, Tacky

Followed by an access indicator
Haven't tested this one, it may be the eleventh character
or it may generate another field
' ' No alternate access
'+' Alternate access
LSfieldsDoc


ListDirectory()
{
	local -a T
	local -i of=0		# Default return in variable
#	OLD_IFS=$IFS		# Using BASH default ' \t\n'

	case "$#" in
	3)	case "$1" in
		-of)	of=1 ; shift ;;
		 * )	return 1 ;;
		esac ;;
	2)	: ;;		# Poor man's "continue"
	*)	return 1 ;;
	esac

	# NOTE: the (ls) command is NOT quoted (")
	T=( $(ls --inode --ignore-backups --almost-all --directory \
	--full-time --color=none --time=status --sort=none \
	--format=long $1) )

	case $of in
	# Assign T back to the array whose name was passed as $2
		0) eval $2=\( \"\$\{T\[@\]\}\" \) ;;
	# Write T into filename passed as $2
		1) echo "${T[@]}" > "$2" ;;
	esac
	return 0
   }

# # # # # Is that string a legal number? # # # # #
#
#	IsNumber "Var"
# # # # # There has to be a better way, sigh...

IsNumber()
{
	local -i int
	if [ $# -eq 0 ]
	then
		return 1
	else
		(let int=$1)  2>/dev/null
		return $?	# Exit status of the let thread
	fi
}

# # # # # Index Filesystem Directory Information # # # # #
#
#	IndexList "Field-Array-Name" "Index-Array-Name"
# or
#	IndexList -if Field-Array-Filename Index-Array-Name
#	IndexList -of Field-Array-Name Index-Array-Filename
#	IndexList -if -of Field-Array-Filename Index-Array-Filename
# # # # #

: <<IndexListDoc
Walk an array of directory fields produced by ListDirectory

Having suppressed the line breaks in an otherwise line oriented
report, build an index to the array element which starts each line.

Each line gets two index entries, the first element of each line
(inode) and the element that holds the pathname of the file.

The first index entry pair (Line-Number==0) are informational:
Index-Array-Name[0] : Number of "Lines" indexed
Index-Array-Name[1] : "Current Line" pointer into Index-Array-Name

The following index pairs (if any) hold element indexes into
the Field-Array-Name per:
Index-Array-Name[Line-Number * 2] : The "inode" field element.
NOTE: This distance may be either +11 or +12 elements.
Index-Array-Name[(Line-Number * 2) + 1] : The "pathname" element.
NOTE: This distance may be a variable number of elements.
Next line index pair for Line-Number+1.
IndexListDoc



IndexList()
{
	local -a LIST			# Local of listname passed
	local -a -i INDEX=( 0 0 )	# Local of index to return
	local -i Lidx Lcnt
	local -i if=0 of=0		# Default to variable names

	case "$#" in			# Simplistic option testing
		0) return 1 ;;
		1) return 1 ;;
		2) : ;;			# Poor man's continue
		3) case "$1" in
			-if) if=1 ;;
			-of) of=1 ;;
			 * ) return 1 ;;
		   esac ; shift ;;
		4) if=1 ; of=1 ; shift ; shift ;;
		*) return 1
	esac

	# Make local copy of list
	case "$if" in
		0) eval LIST=\( \"\$\{$1\[@\]\}\" \) ;;
		1) LIST=( $(cat $1) ) ;;
	esac

	# Grok (grope?) the array
	Lcnt=${#LIST[@]}
	Lidx=0
	until (( Lidx >= Lcnt ))
	do
	if IsNumber ${LIST[$Lidx]}
	then
		local -i inode name
		local ft
		inode=Lidx
		local m=${LIST[$Lidx+2]}	# Hard Links field
		ft=${LIST[$Lidx+1]:0:1} 	# Fast-Stat
		case $ft in
		b)	((Lidx+=12)) ;;		# Block device
		c)	((Lidx+=12)) ;;		# Character device
		*)	((Lidx+=11)) ;;		# Anything else
		esac
		name=Lidx
		case $ft in
		-)	((Lidx+=1)) ;;		# The easy one
		b)	((Lidx+=1)) ;;		# Block device
		c)	((Lidx+=1)) ;;		# Character device
		d)	((Lidx+=1)) ;;		# The other easy one
		l)	((Lidx+=3)) ;;		# At LEAST two more fields
#  A little more elegance here would handle pipes,
#+ sockets, deleted files - later.
		*)	until IsNumber ${LIST[$Lidx]} || ((Lidx >= Lcnt))
			do
				((Lidx+=1))
			done
			;;			# Not required
		esac
		INDEX[${#INDEX[*]}]=$inode
		INDEX[${#INDEX[*]}]=$name
		INDEX[0]=${INDEX[0]}+1		# One more "line" found
# echo "Line: ${INDEX[0]} Type: $ft Links: $m Inode: \
# ${LIST[$inode]} Name: ${LIST[$name]}"

	else
		((Lidx+=1))
	fi
	done
	case "$of" in
		0) eval $2=\( \"\$\{INDEX\[@\]\}\" \) ;;
		1) echo "${INDEX[@]}" > "$2" ;;
	esac
	return 0				# What could go wrong?
}

# # # # # Content Identify File # # # # #
#
#	DigestFile Input-Array-Name Digest-Array-Name
# or
#	DigestFile -if Input-FileName Digest-Array-Name
# # # # #

# Here document used as a comment block.
: <<DigestFilesDoc

The key (no pun intended) to a Unified Content File System (UCFS)
is to distinguish the files in the system based on their content.
Distinguishing files by their name is just, so, 20th Century.

The content is distinguished by computing a checksum of that content.
This version uses the md5sum program to generate a 128 bit checksum
representative of the file's contents.
There is a chance that two files having different content might
generate the same checksum using md5sum (or any checksum).  Should
that become a problem, then the use of md5sum can be replace by a
cyrptographic signature.  But until then...

The md5sum program is documented as outputting three fields (and it
does), but when read it appears as two fields (array elements).  This
is caused by the lack of whitespace between the second and third field.
So this function gropes the md5sum output and returns:
	[0]	32 character checksum in hexidecimal (UCFS filename)
	[1]	Single character: ' ' text file, '*' binary file
	[2]	Filesystem (20th Century Style) name
	Note: That name may be the character '-' indicating STDIN read.

DigestFilesDoc



DigestFile()
{
	local if=0		# Default, variable name
	local -a T1 T2

	case "$#" in
	3)	case "$1" in
		-if)	if=1 ; shift ;;
		 * )	return 1 ;;
		esac ;;
	2)	: ;;		# Poor man's "continue"
	*)	return 1 ;;
	esac

	case $if in
	0) eval T1=\( \"\$\{$1\[@\]\}\" \)
	   T2=( $(echo ${T1[@]} | md5sum -) )
	   ;;
	1) T2=( $(md5sum $1) )
	   ;;
	esac

	case ${#T2[@]} in
	0) return 1 ;;
	1) return 1 ;;
	2) case ${T2[1]:0:1} in		# SanScrit-2.0.5
	   \*) T2[${#T2[@]}]=${T2[1]:1}
	       T2[1]=\*
	       ;;
	    *) T2[${#T2[@]}]=${T2[1]}
	       T2[1]=" "
	       ;;
	   esac
	   ;;
	3) : ;; # Assume it worked
	*) return 1 ;;
	esac

	local -i len=${#T2[0]}
	if [ $len -ne 32 ] ; then return 1 ; fi
	eval $2=\( \"\$\{T2\[@\]\}\" \)
}

# # # # # Locate File # # # # #
#
#	LocateFile [-l] FileName Location-Array-Name
# or
#	LocateFile [-l] -of FileName Location-Array-FileName
# # # # #

# A file location is Filesystem-id and inode-number

# Here document used as a comment block.
: <<StatFieldsDoc
	Based on stat, version 2.2
	stat -t and stat -lt fields
	[0]	name
	[1]	Total size
		File - number of bytes
		Symbolic link - string length of pathname
	[2]	Number of (512 byte) blocks allocated
	[3]	File type and Access rights (hex)
	[4]	User ID of owner
	[5]	Group ID of owner
	[6]	Device number
	[7]	Inode number
	[8]	Number of hard links
	[9]	Device type (if inode device) Major
	[10]	Device type (if inode device) Minor
	[11]	Time of last access
		May be disabled in 'mount' with noatime
		atime of files changed by exec, read, pipe, utime, mknod (mmap?)
		atime of directories changed by addition/deletion of files
	[12]	Time of last modification
		mtime of files changed by write, truncate, utime, mknod
		mtime of directories changed by addtition/deletion of files
	[13]	Time of last change
		ctime reflects time of changed inode information (owner, group
		permissions, link count
-*-*- Per:
	Return code: 0
	Size of array: 14
	Contents of array
	Element 0: /home/mszick
	Element 1: 4096
	Element 2: 8
	Element 3: 41e8
	Element 4: 500
	Element 5: 500
	Element 6: 303
	Element 7: 32385
	Element 8: 22
	Element 9: 0
	Element 10: 0
	Element 11: 1051221030
	Element 12: 1051214068
	Element 13: 1051214068

	For a link in the form of linkname -> realname
	stat -t  linkname returns the linkname (link) information
	stat -lt linkname returns the realname information

	stat -tf and stat -ltf fields
	[0]	name
	[1]	ID-0?		# Maybe someday, but Linux stat structure
	[2]	ID-0?		# does not have either LABEL nor UUID
				# fields, currently information must come
				# from file-system specific utilities
	These will be munged into:
	[1]	UUID if possible
	[2]	Volume Label if possible
	Note: 'mount -l' does return the label and could return the UUID

	[3]	Maximum length of filenames
	[4]	Filesystem type
	[5]	Total blocks in the filesystem
	[6]	Free blocks
	[7]	Free blocks for non-root user(s)
	[8]	Block size of the filesystem
	[9]	Total inodes
	[10]	Free inodes

-*-*- Per:
	Return code: 0
	Size of array: 11
	Contents of array
	Element 0: /home/mszick
	Element 1: 0
	Element 2: 0
	Element 3: 255
	Element 4: ef53
	Element 5: 2581445
	Element 6: 2277180
	Element 7: 2146050
	Element 8: 4096
	Element 9: 1311552
	Element 10: 1276425

StatFieldsDoc


#	LocateFile [-l] FileName Location-Array-Name
#	LocateFile [-l] -of FileName Location-Array-FileName

LocateFile()
{
	local -a LOC LOC1 LOC2
	local lk="" of=0

	case "$#" in
	0) return 1 ;;
	1) return 1 ;;
	2) : ;;
	*) while (( "$#" > 2 ))
	   do
	      case "$1" in
	       -l) lk=-1 ;;
	      -of) of=1 ;;
	        *) return 1 ;;
	      esac
	   shift
           done ;;
	esac

# More Sanscrit-2.0.5
      # LOC1=( $(stat -t $lk $1) )
      # LOC2=( $(stat -tf $lk $1) )
      # Uncomment above two lines if system has "stat" command installed.
	LOC=( ${LOC1[@]:0:1} ${LOC1[@]:3:11}
	      ${LOC2[@]:1:2} ${LOC2[@]:4:1} )

	case "$of" in
		0) eval $2=\( \"\$\{LOC\[@\]\}\" \) ;;
		1) echo "${LOC[@]}" > "$2" ;;
	esac
	return 0
# Which yields (if you are lucky, and have "stat" installed)
# -*-*- Location Discriptor -*-*-
#	Return code: 0
#	Size of array: 15
#	Contents of array
#	Element 0: /home/mszick		20th Century name
#	Element 1: 41e8			Type and Permissions
#	Element 2: 500			User
#	Element 3: 500			Group
#	Element 4: 303			Device
#	Element 5: 32385		inode
#	Element 6: 22			Link count
#	Element 7: 0			Device Major
#	Element 8: 0			Device Minor
#	Element 9: 1051224608		Last Access
#	Element 10: 1051214068		Last Modify
#	Element 11: 1051214068		Last Status
#	Element 12: 0			UUID (to be)
#	Element 13: 0			Volume Label (to be)
#	Element 14: ef53		Filesystem type
}



# And then there was some test code

ListArray() # ListArray Name
{
	local -a Ta

	eval Ta=\( \"\$\{$1\[@\]\}\" \)
	echo
	echo "-*-*- List of Array -*-*-"
	echo "Size of array $1: ${#Ta[*]}"
	echo "Contents of array $1:"
	for (( i=0 ; i<${#Ta[*]} ; i++ ))
	do
	    echo -e "\tElement $i: ${Ta[$i]}"
	done
	return 0
}

declare -a CUR_DIR
# For small arrays
ListDirectory "${PWD}" CUR_DIR
ListArray CUR_DIR

declare -a DIR_DIG
DigestFile CUR_DIR DIR_DIG
echo "The new \"name\" (checksum) for ${CUR_DIR[9]} is ${DIR_DIG[0]}"

declare -a DIR_ENT
# BIG_DIR # For really big arrays - use a temporary file in ramdisk
# BIG-DIR # ListDirectory -of "${CUR_DIR[11]}/*" "/tmpfs/junk2"
ListDirectory "${CUR_DIR[11]}/*" DIR_ENT

declare -a DIR_IDX
# BIG-DIR # IndexList -if "/tmpfs/junk2" DIR_IDX
IndexList DIR_ENT DIR_IDX

declare -a IDX_DIG
# BIG-DIR # DIR_ENT=( $(cat /tmpfs/junk2) )
# BIG-DIR # DigestFile -if /tmpfs/junk2 IDX_DIG
DigestFile DIR_ENT IDX_DIG
# Small (should) be able to parallize IndexList & DigestFile
# Large (should) be able to parallize IndexList & DigestFile & the assignment
echo "The \"name\" (checksum) for the contents of ${PWD} is ${IDX_DIG[0]}"

declare -a FILE_LOC
LocateFile ${PWD} FILE_LOC
ListArray FILE_LOC

exit 0

StИphane Chazelas demonstrates object-oriented programming in a Bash script.

Example A-21. Object-oriented database

#!/bin/bash
# obj-oriented.sh: Object-oriented programming in a shell script.
# Script by Stephane Chazelas.

#  Important Note:
#  --------- ----
#  If running this script under version 3 or later of Bash,
#+ replace all periods in function names with a "legal" character,
#+ for example, an underscore.


person.new()        # Looks almost like a class declaration in C++.
{
  local obj_name=$1 name=$2 firstname=$3 birthdate=$4

  eval "$obj_name.set_name() {
          eval \"$obj_name.get_name() {
                   echo \$1
                 }\"
        }"

  eval "$obj_name.set_firstname() {
          eval \"$obj_name.get_firstname() {
                   echo \$1
                 }\"
        }"

  eval "$obj_name.set_birthdate() {
          eval \"$obj_name.get_birthdate() {
            echo \$1
          }\"
          eval \"$obj_name.show_birthdate() {
            echo \$(date -d \"1/1/1970 0:0:\$1 GMT\")
          }\"
          eval \"$obj_name.get_age() {
            echo \$(( (\$(date +%s) - \$1) / 3600 / 24 / 365 ))
          }\"
        }"

  $obj_name.set_name $name
  $obj_name.set_firstname $firstname
  $obj_name.set_birthdate $birthdate
}

echo

person.new self Bozeman Bozo 101272413
# Create an instance of "person.new" (actually passing args to the function).

self.get_firstname       #   Bozo
self.get_name            #   Bozeman
self.get_age             #   28
self.get_birthdate       #   101272413
self.show_birthdate      #   Sat Mar 17 20:13:33 MST 1973

echo

#  typeset -f
#+ to see the created functions (careful, it scrolls off the page).

exit 0

Mariusz Gniazdowski contributed a hash library for use in scripts.

Example A-22. Library of hash functions

# Hash:
# Hash function library
# Author: Mariusz Gniazdowski <mariusz.gn-at-gmail.com>
# Date: 2005-04-07

# Functions making emulating hashes in Bash a little less painful.


#    Limitations:
#  * Only global variables are supported.
#  * Each hash instance generates one global variable per value.
#  * Variable names collisions are possible
#+   if you define variable like __hash__hashname_key
#  * Keys must use chars that can be part of a Bash variable name
#+   (no dashes, periods, etc.).
#  * The hash is created as a variable:
#    ... hashname_keyname
#    So if somone will create hashes like:
#      myhash_ + mykey = myhash__mykey
#      myhash + _mykey = myhash__mykey
#    Then there will be a collision.
#    (This should not pose a major problem.)


Hash_config_varname_prefix=__hash__


# Emulates:  hash[key]=value
#
# Params:
# 1 - hash
# 2 - key
# 3 - value
function hash_set {
	eval "${Hash_config_varname_prefix}${1}_${2}=\"${3}\""
}


# Emulates:  value=hash[key]
#
# Params:
# 1 - hash
# 2 - key
# 3 - value (name of global variable to set)
function hash_get_into {
	eval "$3=\"\$${Hash_config_varname_prefix}${1}_${2}\""
}


# Emulates:  echo hash[key]
#
# Params:
# 1 - hash
# 2 - key
# 3 - echo params (like -n, for example)
function hash_echo {
	eval "echo $3 \"\$${Hash_config_varname_prefix}${1}_${2}\""
}


# Emulates:  hash1[key1]=hash2[key2]
#
# Params:
# 1 - hash1
# 2 - key1
# 3 - hash2
# 4 - key2
function hash_copy {
eval "${Hash_config_varname_prefix}${1}_${2}\
=\"\$${Hash_config_varname_prefix}${3}_${4}\""
}


# Emulates:  hash[keyN-1]=hash[key2]=...hash[key1]
#
# Copies first key to rest of keys.
#
# Params:
# 1 - hash1
# 2 - key1
# 3 - key2
# . . .
# N - keyN
function hash_dup {
  local hashName="$1" keyName="$2"
  shift 2
  until [ ${#} -le 0 ]; do
    eval "${Hash_config_varname_prefix}${hashName}_${1}\
=\"\$${Hash_config_varname_prefix}${hashName}_${keyName}\""
  shift;
  done;
}


# Emulates:  unset hash[key]
#
# Params:
# 1 - hash
# 2 - key
function hash_unset {
	eval "unset ${Hash_config_varname_prefix}${1}_${2}"
}


# Emulates something similar to:  ref=&hash[key]
#
# The reference is name of the variable in which value is held.
#
# Params:
# 1 - hash
# 2 - key
# 3 - ref - Name of global variable to set.
function hash_get_ref_into {
	eval "$3=\"${Hash_config_varname_prefix}${1}_${2}\""
}


# Emulates something similar to:  echo &hash[key]
#
# That reference is name of variable in which value is held.
#
# Params:
# 1 - hash
# 2 - key
# 3 - echo params (like -n for example)
function hash_echo_ref {
	eval "echo $3 \"${Hash_config_varname_prefix}${1}_${2}\""
}



# Emulates something similar to:  $$hash[key](param1, param2, ...)
#
# Params:
# 1 - hash
# 2 - key
# 3,4, ... - Function parameters
function hash_call {
  local hash key
  hash=$1
  key=$2
  shift 2
  eval "eval \"\$${Hash_config_varname_prefix}${hash}_${key} \\\"\\\$@\\\"\""
}


# Emulates something similar to:  isset(hash[key]) or hash[key]==NULL
#
# Params:
# 1 - hash
# 2 - key
# Returns:
# 0 - there is such key
# 1 - there is no such key
function hash_is_set {
  eval "if [[ \"\${${Hash_config_varname_prefix}${1}_${2}-a}\" = \"a\" && 
  \"\${${Hash_config_varname_prefix}${1}_${2}-b}\" = \"b\" ]]
    then return 1; else return 0; fi"
}


# Emulates something similar to:
#   foreach($hash as $key => $value) { fun($key,$value); }
#
# It is possible to write different variations of this function.
# Here we use a function call to make it as "generic" as possible.
#
# Params:
# 1 - hash
# 2 - function name
function hash_foreach {
  local keyname oldIFS="$IFS"
  IFS=' '
  for i in $(eval "echo \${!${Hash_config_varname_prefix}${1}_*}"); do
    keyname=$(eval "echo \${i##${Hash_config_varname_prefix}${1}_}")
    eval "$2 $keyname \"\$$i\""
  done
IFS="$oldIFS"
}

#  NOTE: In lines 103 and 116, ampersand changed.
#  But, it doesn't matter, because these are comment lines anyhow.

Here is an example script using the foregoing hash library.

Example A-23. Colorizing text using hash functions

#!/bin/bash
# hash-example.sh: Colorizing text.
# Author: Mariusz Gniazdowski <mariusz.gn-at-gmail.com>

. Hash.lib      # Load the library of functions.

hash_set colors red          "\033[0;31m"
hash_set colors blue         "\033[0;34m"
hash_set colors light_blue   "\033[1;34m"
hash_set colors light_red    "\033[1;31m"
hash_set colors cyan         "\033[0;36m"
hash_set colors light_green  "\033[1;32m"
hash_set colors light_gray   "\033[0;37m"
hash_set colors green        "\033[0;32m"
hash_set colors yellow       "\033[1;33m"
hash_set colors light_purple "\033[1;35m"
hash_set colors purple       "\033[0;35m"
hash_set colors reset_color  "\033[0;00m"


# $1 - keyname
# $2 - value
try_colors() {
	echo -en "$2"
	echo "This line is $1."
}
hash_foreach colors try_colors
hash_echo colors reset_color -en

echo -e '\nLet us overwrite some colors with yellow.\n'
# It's hard to read yellow text on some terminals.
hash_dup colors yellow   red light_green blue green light_gray cyan
hash_foreach colors try_colors
hash_echo colors reset_color -en

echo -e '\nLet us delete them and try colors once more . . .\n'

for i in red light_green blue green light_gray cyan; do
	hash_unset colors $i
done
hash_foreach colors try_colors
hash_echo colors reset_color -en

hash_set other txt "Other examples . . ."
hash_echo other txt
hash_get_into other txt text
echo $text

hash_set other my_fun try_colors
hash_call other my_fun   purple "`hash_echo colors purple`"
hash_echo colors reset_color -en

echo; echo "Back to normal?"; echo

exit $?

#  On some terminals, the "light" colors print in bold,
#  and end up looking darker than the normal ones.
#  Why is this? 

An example illustrating the mechanics of hashing, but from a different point of view.

Example A-24. More on hash functions

#!/bin/bash
# $Id: ha.sh,v 1.2 2005/04/21 23:24:26 oliver Exp $
# Copyright 2005 Oliver Beckstein
# Released under the GNU Public License
# Author of script granted permission for inclusion in ABS Guide.
# (Thank you!)

#----------------------------------------------------------------
# pseudo hash based on indirect parameter expansion
# API: access through functions:
# 
# create the hash:
#  
#      newhash Lovers
#
# add entries (note single quotes for spaces)
#    
#      addhash Lovers Tristan Isolde
#      addhash Lovers 'Romeo Montague' 'Juliet Capulet'
#
# access value by key
#
#      gethash Lovers Tristan   ---->  Isolde
#
# show all keys
#
#      keyshash Lovers         ----> 'Tristan'  'Romeo Montague'
#
#
# Convention: instead of perls' foo{bar} = boing' syntax,
# use
#       '_foo_bar=boing' (two underscores, no spaces)
#
# 1) store key   in _NAME_keys[]
# 2) store value in _NAME_values[] using the same integer index
# The integer index for the last entry is _NAME_ptr
#
# NOTE: No error or sanity checks, just bare bones.


function _inihash () {
    # private function
    # call at the beginning of each procedure
    # defines: _keys _values _ptr
    #
    # Usage: _inihash NAME
    local name=$1
    _keys=_${name}_keys
    _values=_${name}_values
    _ptr=_${name}_ptr
}

function newhash () {
    # Usage: newhash NAME
    #        NAME should not contain spaces or dots.
    #        Actually: it must be a legal name for a Bash variable.
    # We rely on Bash automatically recognising arrays.
    local name=$1 
    local _keys _values _ptr
    _inihash ${name}
    eval ${_ptr}=0
}


function addhash () {
    # Usage: addhash NAME KEY 'VALUE with spaces'
    #        arguments with spaces need to be quoted with single quotes ''
    local name=$1 k="$2" v="$3" 
    local _keys _values _ptr
    _inihash ${name}

    #echo "DEBUG(addhash): ${_ptr}=${!_ptr}"

    eval let ${_ptr}=${_ptr}+1
    eval "$_keys[${!_ptr}]=\"${k}\""
    eval "$_values[${!_ptr}]=\"${v}\""
}

function gethash () {
    #  Usage: gethash NAME KEY
    #         Returns boing
    #         ERR=0 if entry found, 1 otherwise
    #  That's not a proper hash --
    #+ we simply linearly search through the keys.
    local name=$1 key="$2" 
    local _keys _values _ptr 
    local k v i found h
    _inihash ${name}
    
    # _ptr holds the highest index in the hash
    found=0

    for i in $(seq 1 ${!_ptr}); do
	h="\${${_keys}[${i}]}"  #  Safer to do it in two steps,
	eval k=${h}             #+ especially when quoting for spaces.
	if [ "${k}" = "${key}" ]; then found=1; break; fi
    done;

    [ ${found} = 0 ] && return 1;
    # else: i is the index that matches the key
    h="\${${_values}[${i}]}"
    eval echo "${h}"
    return 0;	
}

function keyshash () {
    # Usage: keyshash NAME
    # Returns list of all keys defined for hash name.
    local name=$1 key="$2" 
    local _keys _values _ptr 
    local k i h
    _inihash ${name}
    
    # _ptr holds the highest index in the hash
    for i in $(seq 1 ${!_ptr}); do
	h="\${${_keys}[${i}]}"   #  Safer to do it in two steps,
	eval k=${h}              #+ especially when quoting for spaces.
	echo -n "'${k}' "
    done;
}


# -----------------------------------------------------------------------

# Now, let's test it.
# (Per comments at the beginning of the script.)
newhash Lovers
addhash Lovers Tristan Isolde
addhash Lovers 'Romeo Montague' 'Juliet Capulet'

# Output results.
echo
gethash Lovers Tristan      # Isolde
echo
keyshash Lovers             # 'Tristan' 'Romeo Montague'
echo; echo


exit 0

# Exercise:
# --------

# Add error checks to the functions.

Now for a script that installs and mounts those cute USB keychain solid-state "hard drives."

Example A-25. Mounting USB keychain storage devices

#!/bin/bash
# ==> usb.sh
# ==> Script for mounting and installing pen/keychain USB storage devices.
# ==> Runs as root at system startup (see below).
# ==>
# ==> Newer Linux distros (2004 or later) autodetect
# ==> and install USB pen drives, and therefore don't need this script.
# ==> But, it's still instructive.
 
#  This code is free software covered by GNU GPL license version 2 or above.
#  Please refer to http://www.gnu.org/ for the full license text.
#
#  Some code lifted from usb-mount by Michael Hamilton's usb-mount (LGPL)
#+ see http://users.actrix.co.nz/michael/usbmount.html
#
#  INSTALL
#  -------
#  Put this in /etc/hotplug/usb/diskonkey.
#  Then look in /etc/hotplug/usb.distmap, and copy all usb-storage entries
#+ into /etc/hotplug/usb.usermap, substituting "usb-storage" for "diskonkey".
#  Otherwise this code is only run during the kernel module invocation/removal
#+ (at least in my tests), which defeats the purpose.
#
#  TODO
#  ----
#  Handle more than one diskonkey device at one time (e.g. /dev/diskonkey1
#+ and /mnt/diskonkey1), etc. The biggest problem here is the handling in
#+ devlabel, which I haven't yet tried.
#
#  AUTHOR and SUPPORT
#  ------------------
#  Konstantin Riabitsev, <icon linux duke edu>.
#  Send any problem reports to my email address at the moment.
#
# ==> Comments added by ABS Guide author.



SYMLINKDEV=/dev/diskonkey
MOUNTPOINT=/mnt/diskonkey
DEVLABEL=/sbin/devlabel
DEVLABELCONFIG=/etc/sysconfig/devlabel
IAM=$0

##
# Functions lifted near-verbatim from usb-mount code.
#
function allAttachedScsiUsb {
  find /proc/scsi/ -path '/proc/scsi/usb-storage*' -type f |
  xargs grep -l 'Attached: Yes'
}
function scsiDevFromScsiUsb {
  echo $1 | awk -F"[-/]" '{ n=$(NF-1);
  print "/dev/sd" substr("abcdefghijklmnopqrstuvwxyz", n+1, 1) }'
}

if [ "${ACTION}" = "add" ] && [ -f "${DEVICE}" ]; then
    ##
    # lifted from usbcam code.
    #
    if [ -f /var/run/console.lock ]; then
        CONSOLEOWNER=`cat /var/run/console.lock`
    elif [ -f /var/lock/console.lock ]; then
        CONSOLEOWNER=`cat /var/lock/console.lock`
    else
        CONSOLEOWNER=
    fi
    for procEntry in $(allAttachedScsiUsb); do
        scsiDev=$(scsiDevFromScsiUsb $procEntry)
        #  Some bug with usb-storage?
        #  Partitions are not in /proc/partitions until they are accessed
        #+ somehow.
        /sbin/fdisk -l $scsiDev >/dev/null
        ##
        #  Most devices have partitioning info, so the data would be on
        #+ /dev/sd?1. However, some stupider ones don't have any partitioning
        #+ and use the entire device for data storage. This tries to
        #+ guess semi-intelligently if we have a /dev/sd?1 and if not, then
        #+ it uses the entire device and hopes for the better.
        #
        if grep -q `basename $scsiDev`1 /proc/partitions; then
            part="$scsiDev""1"
        else
            part=$scsiDev
        fi
        ##
        #  Change ownership of the partition to the console user so they can
        #+ mount it.
        #
        if [ ! -z "$CONSOLEOWNER" ]; then
            chown $CONSOLEOWNER:disk $part
        fi
        ##
        # This checks if we already have this UUID defined with devlabel.
        # If not, it then adds the device to the list.
        #
        prodid=`$DEVLABEL printid -d $part`
        if ! grep -q $prodid $DEVLABELCONFIG; then
            # cross our fingers and hope it works
            $DEVLABEL add -d $part -s $SYMLINKDEV 2>/dev/null
        fi
        ##
        # Check if the mount point exists and create if it doesn't.
        #
        if [ ! -e $MOUNTPOINT ]; then
            mkdir -p $MOUNTPOINT
        fi
        ##
        # Take care of /etc/fstab so mounting is easy.
        #
        if ! grep -q "^$SYMLINKDEV" /etc/fstab; then
            # Add an fstab entry
            echo -e \
                "$SYMLINKDEV\t\t$MOUNTPOINT\t\tauto\tnoauto,owner,kudzu 0 0" \
                >> /etc/fstab
        fi
    done
    if [ ! -z "$REMOVER" ]; then
        ##
        # Make sure this script is triggered on device removal.
        #
        mkdir -p `dirname $REMOVER`
        ln -s $IAM $REMOVER
    fi
elif [ "${ACTION}" = "remove" ]; then
    ##
    # If the device is mounted, unmount it cleanly.
    #
    if grep -q "$MOUNTPOINT" /etc/mtab; then
        # unmount cleanly
        umount -l $MOUNTPOINT
    fi
    ##
    # Remove it from /etc/fstab if it's there.
    #
    if grep -q "^$SYMLINKDEV" /etc/fstab; then
        grep -v "^$SYMLINKDEV" /etc/fstab > /etc/.fstab.new
        mv -f /etc/.fstab.new /etc/fstab
    fi
fi

exit 0

Converting a text file to HTML format.

Example A-26. Converting to HTML

#!/bin/bash
# tohtml.sh [v. 0.2, reldate: 06/26/08, still buggy]

# Convert a text file to HTML format.
# Author: Mendel Cooper
# License: GPL3
# Usage: sh tohtml.sh < textfile > htmlfile
# Script can easily be modified to accept source and target filenames.

#    Assumptions:
# 1) Paragraphs in (target) text file are separated by a blank line.
# 2) Jpeg images (*.jpg) are located in "images" subdirectory.
#    In the target file, the image names are enclosed in square brackets,
#    for example, [image01.jpg].
# 3) Emphasized (italic) phrases begin with a space+underscore
#+   or the first character on the line is an underscore,
#+   and end with an underscore+space or underscore+end-of-line.


# Settings
FNTSIZE=2        # Small-medium font size
IMGDIR="images"  # Image directory
# Headers
HDR01='<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">'
HDR02='<!-- Converted to HTML by ***tohtml.sh*** script -->'
HDR03='<!-- script author: M. Leo Cooper <thegrendel.abs@gmail.com> -->'
HDR10='<html>'
HDR11='<head>'
HDR11a='</head>'
HDR12a='<title>'
HDR12b='</title>'
HDR121='<META NAME="GENERATOR" CONTENT="tohtml.sh script">'
HDR13='<body bgcolor="#dddddd">'   # Change background color to suit.
HDR14a='<font size='
HDR14b='>'
# Footers
FTR10='</body>'
FTR11='</html>'
# Tags
BOLD="<b>"
CENTER="<center>"
END_CENTER="</center>"
LF="<br>"


write_headers ()
  {
  echo "$HDR01"
  echo
  echo "$HDR02"
  echo "$HDR03"
  echo
  echo
  echo "$HDR10"
  echo "$HDR11"
  echo "$HDR121"
  echo "$HDR11a"
  echo "$HDR13"
  echo
  echo -n "$HDR14a"
  echo -n "$FNTSIZE"
  echo "$HDR14b"
  echo
  echo "$BOLD"        # Everything in bold (more easily readable).
  }


process_text ()
  {
  while read line     # Read one line at a time.
  do
    {
    if [ ! "$line" ]  # Blank line?
    then              # Then new paragraph must follow.
      echo
      echo "$LF"      # Insert two <br> tags.
      echo "$LF"
      echo
      continue        # Skip the underscore test.
    else              # Otherwise . . .

      if [[ "$line" =~ "\[*jpg\]" ]]  # Is a graphic?
      then                            # Strip away brackets.
        temp=$( echo "$line" | sed -e 's/\[//' -e 's/\]//' )
        line=""$CENTER" <img src="\"$IMGDIR"/$temp\"> "$END_CENTER" "
                                      # Add image tag.
                                      # And, center it.
      fi

    fi


    echo "$line" | grep -q _
    if [ "$?" -eq 0 ]    # If line contains underscore ...
    then
      # ===================================================
      # Convert underscored phrase to italics.
      temp=$( echo "$line" |
              sed -e 's/ _/ <i>/' -e 's/_/<\/i> /' |
              sed -e 's/^_/<i>/'  -e 's/_/<\/i>/' )
      #  Process only underscores prefixed by space,
      #+ or at beginning or end of line.
      #  Do not convert underscores embedded within a word!
      line="$temp"
      # Slows script execution. Can be optimized?
      # ===================================================
    fi


   
    echo
    echo "$line"
    echo
    } # End while
  done
  }   # End process_text ()


write_footers ()  # Termination tags.
  {
  echo "$FTR10"
  echo "$FTR11"
  }


# main () {
# =========
write_headers
process_text
write_footers
# =========
#         }

exit $?

#  Exercises:
#  ---------
#  1) Fixup: Check for closing underscore before a comma or period.
#  2) Add a test for the presence of a closing underscore
#+    in phrases to be italicized.

Here is something to warm the hearts of webmasters and mistresses: a script that saves weblogs.

Example A-27. Preserving weblogs

#!/bin/bash
# archiveweblogs.sh v1.0

# Troy Engel <tengel@fluid.com>
# Slightly modified by document author.
# Used with permission.
#
#  This script will preserve the normally rotated and
#+ thrown away weblogs from a default RedHat/Apache installation.
#  It will save the files with a date/time stamp in the filename,
#+ bzipped, to a given directory.
#
#  Run this from crontab nightly at an off hour,
#+ as bzip2 can suck up some serious CPU on huge logs:
#  0 2 * * * /opt/sbin/archiveweblogs.sh


PROBLEM=66

# Set this to your backup dir.
BKP_DIR=/opt/backups/weblogs

# Default Apache/RedHat stuff
LOG_DAYS="4 3 2 1"
LOG_DIR=/var/log/httpd
LOG_FILES="access_log error_log"

# Default RedHat program locations
LS=/bin/ls
MV=/bin/mv
ID=/usr/bin/id
CUT=/bin/cut
COL=/usr/bin/column
BZ2=/usr/bin/bzip2

# Are we root?
USER=`$ID -u`
if [ "X$USER" != "X0" ]; then
  echo "PANIC: Only root can run this script!"
  exit $PROBLEM
fi

# Backup dir exists/writable?
if [ ! -x $BKP_DIR ]; then
  echo "PANIC: $BKP_DIR doesn't exist or isn't writable!"
  exit $PROBLEM
fi

# Move, rename and bzip2 the logs
for logday in $LOG_DAYS; do
  for logfile in $LOG_FILES; do
    MYFILE="$LOG_DIR/$logfile.$logday"
    if [ -w $MYFILE ]; then
      DTS=`$LS -lgo --time-style=+%Y%m%d $MYFILE | $COL -t | $CUT -d ' ' -f7`
      $MV $MYFILE $BKP_DIR/$logfile.$DTS
      $BZ2 $BKP_DIR/$logfile.$DTS
    else
      # Only spew an error if the file exits (ergo non-writable).
      if [ -f $MYFILE ]; then
        echo "ERROR: $MYFILE not writable. Skipping."
      fi
    fi
  done
done

exit 0

How to keep the shell from expanding and reinterpreting text strings.

Example A-28. Protecting literal strings

#! /bin/bash
# protect_literal.sh

# set -vx

:<<-'_Protect_Literal_String_Doc'

    Copyright (c) Michael S. Zick, 2003; All Rights Reserved
    License: Unrestricted reuse in any form, for any purpose.
    Warranty: None
    Revision: $ID$

    Documentation redirected to the Bash no-operation.
    Bash will '/dev/null' this block when the script is first read.
    (Uncomment the above set command to see this action.)

    Remove the first (Sha-Bang) line when sourcing this as a library
    procedure.  Also comment out the example use code in the two
    places where shown.


    Usage:
        _protect_literal_str 'Whatever string meets your ${fancy}'
        Just echos the argument to standard out, hard quotes
        restored.

        $(_protect_literal_str 'Whatever string meets your ${fancy}')
        as the right-hand-side of an assignment statement.

    Does:
        As the right-hand-side of an assignment, preserves the
        hard quotes protecting the contents of the literal during
        assignment.

    Notes:
        The strange names (_*) are used to avoid trampling on
        the user's chosen names when this is sourced as a
        library.

_Protect_Literal_String_Doc

# The 'for illustration' function form

_protect_literal_str() {

# Pick an un-used, non-printing character as local IFS.
# Not required, but shows that we are ignoring it.
    local IFS=$'\x1B'               # \ESC character

# Enclose the All-Elements-Of in hard quotes during assignment.
    local tmp=$'\x27'$@$'\x27'
#    local tmp=$'\''$@$'\''         # Even uglier.

    local len=${#tmp}               # Info only.
    echo $tmp is $len long.         # Output AND information.
}

# This is the short-named version.
_pls() {
    local IFS=$'x1B'                # \ESC character (not required)
    echo $'\x27'$@$'\x27'           # Hard quoted parameter glob
}

# :<<-'_Protect_Literal_String_Test'
# # # Remove the above "# " to disable this code. # # #

# See how that looks when printed.
echo
echo "- - Test One - -"
_protect_literal_str 'Hello $user'
_protect_literal_str 'Hello "${username}"'
echo

# Which yields:
# - - Test One - -
# 'Hello $user' is 13 long.
# 'Hello "${username}"' is 21 long.

#  Looks as expected, but why all of the trouble?
#  The difference is hidden inside the Bash internal order
#+ of operations.
#  Which shows when you use it on the RHS of an assignment.

# Declare an array for test values.
declare -a arrayZ

# Assign elements with various types of quotes and escapes.
arrayZ=( zero "$(_pls 'Hello ${Me}')" 'Hello ${You}' "\'Pass: ${pw}\'" )

# Now list that array and see what is there.
echo "- - Test Two - -"
for (( i=0 ; i<${#arrayZ[*]} ; i++ ))
do
    echo  Element $i: ${arrayZ[$i]} is: ${#arrayZ[$i]} long.
done
echo

# Which yields:
# - - Test Two - -
# Element 0: zero is: 4 long.           # Our marker element
# Element 1: 'Hello ${Me}' is: 13 long. # Our "$(_pls '...' )"
# Element 2: Hello ${You} is: 12 long.  # Quotes are missing
# Element 3: \'Pass: \' is: 10 long.    # ${pw} expanded to nothing

# Now make an assignment with that result.
declare -a array2=( ${arrayZ[@]} )

# And print what happened.
echo "- - Test Three - -"
for (( i=0 ; i<${#array2[*]} ; i++ ))
do
    echo  Element $i: ${array2[$i]} is: ${#array2[$i]} long.
done
echo

# Which yields:
# - - Test Three - -
# Element 0: zero is: 4 long.           # Our marker element.
# Element 1: Hello ${Me} is: 11 long.   # Intended result.
# Element 2: Hello is: 5 long.          # ${You} expanded to nothing.
# Element 3: 'Pass: is: 6 long.         # Split on the whitespace.
# Element 4: ' is: 1 long.              # The end quote is here now.

#  Our Element 1 has had its leading and trailing hard quotes stripped.
#  Although not shown, leading and trailing whitespace is also stripped.
#  Now that the string contents are set, Bash will always, internally,
#+ hard quote the contents as required during its operations.

#  Why?
#  Considering our "$(_pls 'Hello ${Me}')" construction:
#  " ... " -> Expansion required, strip the quotes.
#  $( ... ) -> Replace with the result of..., strip this.
#  _pls ' ... ' -> called with literal arguments, strip the quotes.
#  The result returned includes hard quotes; BUT the above processing
#+ has already been done, so they become part of the value assigned.
#
#  Similarly, during further usage of the string variable, the ${Me}
#+ is part of the contents (result) and survives any operations
#  (Until explicitly told to evaluate the string).

#  Hint: See what happens when the hard quotes ($'\x27') are replaced
#+ with soft quotes ($'\x22') in the above procedures.
#  Interesting also is to remove the addition of any quoting.

# _Protect_Literal_String_Test
# # # Remove the above "# " to disable this code. # # #

exit 0

But, what if you want the shell to expand and reinterpret strings?

Example A-29. Unprotecting literal strings

#! /bin/bash
# unprotect_literal.sh

# set -vx

:<<-'_UnProtect_Literal_String_Doc'

    Copyright (c) Michael S. Zick, 2003; All Rights Reserved
    License: Unrestricted reuse in any form, for any purpose.
    Warranty: None
    Revision: $ID$

    Documentation redirected to the Bash no-operation. Bash will
    '/dev/null' this block when the script is first read.
    (Uncomment the above set command to see this action.)

    Remove the first (Sha-Bang) line when sourcing this as a library
    procedure.  Also comment out the example use code in the two
    places where shown.


    Usage:
        Complement of the "$(_pls 'Literal String')" function.
        (See the protect_literal.sh example.)

        StringVar=$(_upls ProtectedSringVariable)

    Does:
        When used on the right-hand-side of an assignment statement;
        makes the substitions embedded in the protected string.

    Notes:
        The strange names (_*) are used to avoid trampling on
        the user's chosen names when this is sourced as a
        library.


_UnProtect_Literal_String_Doc

_upls() {
    local IFS=$'x1B'                # \ESC character (not required)
    eval echo $@                    # Substitution on the glob.
}

# :<<-'_UnProtect_Literal_String_Test'
# # # Remove the above "# " to disable this code. # # #


_pls() {
    local IFS=$'x1B'                # \ESC character (not required)
    echo $'\x27'$@$'\x27'           # Hard quoted parameter glob
}

# Declare an array for test values.
declare -a arrayZ

# Assign elements with various types of quotes and escapes.
arrayZ=( zero "$(_pls 'Hello ${Me}')" 'Hello ${You}' "\'Pass: ${pw}\'" )

# Now make an assignment with that result.
declare -a array2=( ${arrayZ[@]} )

# Which yielded:
# - - Test Three - -
# Element 0: zero is: 4 long            # Our marker element.
# Element 1: Hello ${Me} is: 11 long    # Intended result.
# Element 2: Hello is: 5 long           # ${You} expanded to nothing.
# Element 3: 'Pass: is: 6 long          # Split on the whitespace.
# Element 4: ' is: 1 long               # The end quote is here now.

# set -vx

#  Initialize 'Me' to something for the embedded ${Me} substitution.
#  This needs to be done ONLY just prior to evaluating the
#+ protected string.
#  (This is why it was protected to begin with.)

Me="to the array guy."

# Set a string variable destination to the result.
newVar=$(_upls ${array2[1]})

# Show what the contents are.
echo $newVar

# Do we really need a function to do this?
newerVar=$(eval echo ${array2[1]})
echo $newerVar

#  I guess not, but the _upls function gives us a place to hang
#+ the documentation on.
#  This helps when we forget what a # construction like:
#+ $(eval echo ... ) means.

# What if Me isn't set when the protected string is evaluated?
unset Me
newestVar=$(_upls ${array2[1]})
echo $newestVar

# Just gone, no hints, no runs, no errors.

#  Why in the world?
#  Setting the contents of a string variable containing character
#+ sequences that have a meaning in Bash is a general problem in
#+ script programming.
#
#  This problem is now solved in eight lines of code
#+ (and four pages of description).

#  Where is all this going?
#  Dynamic content Web pages as an array of Bash strings.
#  Content set per request by a Bash 'eval' command
#+ on the stored page template.
#  Not intended to replace PHP, just an interesting thing to do.
###
#  Don't have a webserver application?
#  No problem, check the example directory of the Bash source;
#+ there is a Bash script for that also.

# _UnProtect_Literal_String_Test
# # # Remove the above "# " to disable this code. # # #

exit 0

This interesting script helps hunt down spammers.

Example A-30. Spammer Identification

#!/bin/bash

# $Id: is_spammer.bash,v 1.12.2.11 2004/10/01 21:42:33 mszick Exp $
# Above line is RCS info.

# The latest version of this script is available from http://www.morethan.org.
#
# Spammer-identification
# by Michael S. Zick
# Used in the ABS Guide with permission.



#######################################################
# Documentation
# See also "Quickstart" at end of script.
#######################################################

:<<-'__is_spammer_Doc_'

    Copyright (c) Michael S. Zick, 2004
    License: Unrestricted reuse in any form, for any purpose.
    Warranty: None -{Its a script; the user is on their own.}-

Impatient?
    Application code: goto "# # # Hunt the Spammer' program code # # #"
    Example output: ":<<-'_is_spammer_outputs_'"
    How to use: Enter script name without arguments.
                Or goto "Quickstart" at end of script.

Provides
    Given a domain name or IP(v4) address as input:

    Does an exhaustive set of queries to find the associated
    network resources (short of recursing into TLDs).

    Checks the IP(v4) addresses found against Blacklist
    nameservers.

    If found to be a blacklisted IP(v4) address,
    reports the blacklist text records.
    (Usually hyper-links to the specific report.)

Requires
    A working Internet connection.
    (Exercise: Add check and/or abort if not on-line when running script.)
    Bash with arrays (2.05b+).

    The external program 'dig' --
    a utility program provided with the 'bind' set of programs.
    Specifically, the version which is part of Bind series 9.x
    See: http://www.isc.org

    All usages of 'dig' are limited to wrapper functions,
    which may be rewritten as required.
    See: dig_wrappers.bash for details.
         ("Additional documentation" -- below)

Usage
    Script requires a single argument, which may be:
    1) A domain name;
    2) An IP(v4) address;
    3) A filename, with one name or address per line.

    Script accepts an optional second argument, which may be:
    1) A Blacklist server name;
    2) A filename, with one Blacklist server name per line.

    If the second argument is not provided, the script uses
    a built-in set of (free) Blacklist servers.

    See also, the Quickstart at the end of this script (after 'exit').

Return Codes
    0 - All OK
    1 - Script failure
    2 - Something is Blacklisted

Optional environment variables
    SPAMMER_TRACE
        If set to a writable file,
        script will log an execution flow trace.

    SPAMMER_DATA
        If set to a writable file, script will dump its
        discovered data in the form of GraphViz file.
        See: http://www.research.att.com/sw/tools/graphviz

    SPAMMER_LIMIT
        Limits the depth of resource tracing.

        Default is 2 levels.

        A setting of 0 (zero) means 'unlimited' . . .
          Caution: script might recurse the whole Internet!

        A limit of 1 or 2 is most useful when processing
        a file of domain names and addresses.
        A higher limit can be useful when hunting spam gangs.


Additional documentation
    Download the archived set of scripts
    explaining and illustrating the function contained within this script.
    http://bash.neuralshortcircuit.com/mszick_clf.tar.bz2


Study notes
    This script uses a large number of functions.
    Nearly all general functions have their own example script.
    Each of the example scripts have tutorial level comments.

Scripting project
    Add support for IP(v6) addresses.
    IP(v6) addresses are recognized but not processed.

Advanced project
    Add the reverse lookup detail to the discovered information.

    Report the delegation chain and abuse contacts.

    Modify the GraphViz file output to include the
    newly discovered information.

__is_spammer_Doc_

#######################################################




#### Special IFS settings used for string parsing. ####

# Whitespace == :Space:Tab:Line Feed:Carriage Return:
WSP_IFS=$'\x20'$'\x09'$'\x0A'$'\x0D'

# No Whitespace == Line Feed:Carriage Return
NO_WSP=$'\x0A'$'\x0D'

# Field separator for dotted decimal IP addresses
ADR_IFS=${NO_WSP}'.'

# Array to dotted string conversions
DOT_IFS='.'${WSP_IFS}

# # # Pending operations stack machine # # #
# This set of functions described in func_stack.bash.
# (See "Additional documentation" above.)
# # #

# Global stack of pending operations.
declare -f -a _pending_
# Global sentinel for stack runners
declare -i _p_ctrl_
# Global holder for currently executing function
declare -f _pend_current_

# # # Debug version only - remove for regular use # # #
#
# The function stored in _pend_hook_ is called
# immediately before each pending function is
# evaluated.  Stack clean, _pend_current_ set.
#
# This thingy demonstrated in pend_hook.bash.
declare -f _pend_hook_
# # #

# The do nothing function
pend_dummy() { : ; }

# Clear and initialize the function stack.
pend_init() {
    unset _pending_[@]
    pend_func pend_stop_mark
    _pend_hook_='pend_dummy'  # Debug only.
}

# Discard the top function on the stack.
pend_pop() {
    if [ ${#_pending_[@]} -gt 0 ]
    then
        local -i _top_
        _top_=${#_pending_[@]}-1
        unset _pending_[$_top_]
    fi
}

# pend_func function_name [$(printf '%q\n' arguments)]
pend_func() {
    local IFS=${NO_WSP}
    set -f
    _pending_[${#_pending_[@]}]=$@
    set +f
}

# The function which stops the release:
pend_stop_mark() {
    _p_ctrl_=0
}

pend_mark() {
    pend_func pend_stop_mark
}

# Execute functions until 'pend_stop_mark' . . .
pend_release() {
    local -i _top_             # Declare _top_ as integer.
    _p_ctrl_=${#_pending_[@]}
    while [ ${_p_ctrl_} -gt 0 ]
    do
       _top_=${#_pending_[@]}-1
       _pend_current_=${_pending_[$_top_]}
       unset _pending_[$_top_]
       $_pend_hook_            # Debug only.
       eval $_pend_current_
    done
}

# Drop functions until 'pend_stop_mark' . . .
pend_drop() {
    local -i _top_
    local _pd_ctrl_=${#_pending_[@]}
    while [ ${_pd_ctrl_} -gt 0 ]
    do
       _top_=$_pd_ctrl_-1
       if [ "${_pending_[$_top_]}" == 'pend_stop_mark' ]
       then
           unset _pending_[$_top_]
           break
       else
           unset _pending_[$_top_]
           _pd_ctrl_=$_top_
       fi
    done
    if [ ${#_pending_[@]} -eq 0 ]
    then
        pend_func pend_stop_mark
    fi
}

#### Array editors ####

# This function described in edit_exact.bash.
# (See "Additional documentation," above.)
# edit_exact <excludes_array_name> <target_array_name>
edit_exact() {
    [ $# -eq 2 ] ||
    [ $# -eq 3 ] || return 1
    local -a _ee_Excludes
    local -a _ee_Target
    local _ee_x
    local _ee_t
    local IFS=${NO_WSP}
    set -f
    eval _ee_Excludes=\( \$\{$1\[@\]\} \)
    eval _ee_Target=\( \$\{$2\[@\]\} \)
    local _ee_len=${#_ee_Target[@]}     # Original length.
    local _ee_cnt=${#_ee_Excludes[@]}   # Exclude list length.
    [ ${_ee_len} -ne 0 ] || return 0    # Can't edit zero length.
    [ ${_ee_cnt} -ne 0 ] || return 0    # Can't edit zero length.
    for (( x = 0; x < ${_ee_cnt} ; x++ ))
    do
        _ee_x=${_ee_Excludes[$x]}
        for (( n = 0 ; n < ${_ee_len} ; n++ ))
        do
            _ee_t=${_ee_Target[$n]}
            if [ x"${_ee_t}" == x"${_ee_x}" ]
            then
                unset _ee_Target[$n]     # Discard match.
                [ $# -eq 2 ] && break    # If 2 arguments, then done.
            fi
        done
    done
    eval $2=\( \$\{_ee_Target\[@\]\} \)
    set +f
    return 0
}

# This function described in edit_by_glob.bash.
# edit_by_glob <excludes_array_name> <target_array_name>
edit_by_glob() {
    [ $# -eq 2 ] ||
    [ $# -eq 3 ] || return 1
    local -a _ebg_Excludes
    local -a _ebg_Target
    local _ebg_x
    local _ebg_t
    local IFS=${NO_WSP}
    set -f
    eval _ebg_Excludes=\( \$\{$1\[@\]\} \)
    eval _ebg_Target=\( \$\{$2\[@\]\} \)
    local _ebg_len=${#_ebg_Target[@]}
    local _ebg_cnt=${#_ebg_Excludes[@]}
    [ ${_ebg_len} -ne 0 ] || return 0
    [ ${_ebg_cnt} -ne 0 ] || return 0
    for (( x = 0; x < ${_ebg_cnt} ; x++ ))
    do
        _ebg_x=${_ebg_Excludes[$x]}
        for (( n = 0 ; n < ${_ebg_len} ; n++ ))
        do
            [ $# -eq 3 ] && _ebg_x=${_ebg_x}'*'  #  Do prefix edit
            if [ ${_ebg_Target[$n]:=} ]          #+ if defined & set.
            then
                _ebg_t=${_ebg_Target[$n]/#${_ebg_x}/}
                [ ${#_ebg_t} -eq 0 ] && unset _ebg_Target[$n]
            fi
        done
    done
    eval $2=\( \$\{_ebg_Target\[@\]\} \)
    set +f
    return 0
}

# This function described in unique_lines.bash.
# unique_lines <in_name> <out_name>
unique_lines() {
    [ $# -eq 2 ] || return 1
    local -a _ul_in
    local -a _ul_out
    local -i _ul_cnt
    local -i _ul_pos
    local _ul_tmp
    local IFS=${NO_WSP}
    set -f
    eval _ul_in=\( \$\{$1\[@\]\} \)
    _ul_cnt=${#_ul_in[@]}
    for (( _ul_pos = 0 ; _ul_pos < ${_ul_cnt} ; _ul_pos++ ))
    do
        if [ ${_ul_in[${_ul_pos}]:=} ]      # If defined & not empty
        then
            _ul_tmp=${_ul_in[${_ul_pos}]}
            _ul_out[${#_ul_out[@]}]=${_ul_tmp}
            for (( zap = _ul_pos ; zap < ${_ul_cnt} ; zap++ ))
            do
                [ ${_ul_in[${zap}]:=} ] &&
                [ 'x'${_ul_in[${zap}]} == 'x'${_ul_tmp} ] &&
                    unset _ul_in[${zap}]
            done
        fi
    done
    eval $2=\( \$\{_ul_out\[@\]\} \)
    set +f
    return 0
}

# This function described in char_convert.bash.
# to_lower <string>
to_lower() {
    [ $# -eq 1 ] || return 1
    local _tl_out
    _tl_out=${1//A/a}
    _tl_out=${_tl_out//B/b}
    _tl_out=${_tl_out//C/c}
    _tl_out=${_tl_out//D/d}
    _tl_out=${_tl_out//E/e}
    _tl_out=${_tl_out//F/f}
    _tl_out=${_tl_out//G/g}
    _tl_out=${_tl_out//H/h}
    _tl_out=${_tl_out//I/i}
    _tl_out=${_tl_out//J/j}
    _tl_out=${_tl_out//K/k}
    _tl_out=${_tl_out//L/l}
    _tl_out=${_tl_out//M/m}
    _tl_out=${_tl_out//N/n}
    _tl_out=${_tl_out//O/o}
    _tl_out=${_tl_out//P/p}
    _tl_out=${_tl_out//Q/q}
    _tl_out=${_tl_out//R/r}
    _tl_out=${_tl_out//S/s}
    _tl_out=${_tl_out//T/t}
    _tl_out=${_tl_out//U/u}
    _tl_out=${_tl_out//V/v}
    _tl_out=${_tl_out//W/w}
    _tl_out=${_tl_out//X/x}
    _tl_out=${_tl_out//Y/y}
    _tl_out=${_tl_out//Z/z}
    echo ${_tl_out}
    return 0
}

#### Application helper functions ####

# Not everybody uses dots as separators (APNIC, for example).
# This function described in to_dot.bash
# to_dot <string>
to_dot() {
    [ $# -eq 1 ] || return 1
    echo ${1//[#|@|%]/.}
    return 0
}

# This function described in is_number.bash.
# is_number <input>
is_number() {
    [ "$#" -eq 1 ]    || return 1  # is blank?
    [ x"$1" == 'x0' ] && return 0  # is zero?
    local -i tst
    let tst=$1 2>/dev/null         # else is numeric!
    return $?
}

# This function described in is_address.bash.
# is_address <input>
is_address() {
    [ $# -eq 1 ] || return 1    # Blank ==> false
    local -a _ia_input
    local IFS=${ADR_IFS}
    _ia_input=( $1 )
    if  [ ${#_ia_input[@]} -eq 4 ]  &&
        is_number ${_ia_input[0]}   &&
        is_number ${_ia_input[1]}   &&
        is_number ${_ia_input[2]}   &&
        is_number ${_ia_input[3]}   &&
        [ ${_ia_input[0]} -lt 256 ] &&
        [ ${_ia_input[1]} -lt 256 ] &&
        [ ${_ia_input[2]} -lt 256 ] &&
        [ ${_ia_input[3]} -lt 256 ]
    then
        return 0
    else
        return 1
    fi
}

#  This function described in split_ip.bash.
#  split_ip <IP_address>
#+ <array_name_norm> [<array_name_rev>]
split_ip() {
    [ $# -eq 3 ] ||              #  Either three
    [ $# -eq 2 ] || return 1     #+ or two arguments
    local -a _si_input
    local IFS=${ADR_IFS}
    _si_input=( $1 )
    IFS=${WSP_IFS}
    eval $2=\(\ \$\{_si_input\[@\]\}\ \)
    if [ $# -eq 3 ]
    then
        # Build query order array.
        local -a _dns_ip
        _dns_ip[0]=${_si_input[3]}
        _dns_ip[1]=${_si_input[2]}
        _dns_ip[2]=${_si_input[1]}
        _dns_ip[3]=${_si_input[0]}
        eval $3=\(\ \$\{_dns_ip\[@\]\}\ \)
    fi
    return 0
}

# This function described in dot_array.bash.
# dot_array <array_name>
dot_array() {
    [ $# -eq 1 ] || return 1     # Single argument required.
    local -a _da_input
    eval _da_input=\(\ \$\{$1\[@\]\}\ \)
    local IFS=${DOT_IFS}
    local _da_output=${_da_input[@]}
    IFS=${WSP_IFS}
    echo ${_da_output}
    return 0
}

# This function described in file_to_array.bash
# file_to_array <file_name> <line_array_name>
file_to_array() {
    [ $# -eq 2 ] || return 1  # Two arguments required.
    local IFS=${NO_WSP}
    local -a _fta_tmp_
    _fta_tmp_=( $(cat $1) )
    eval $2=\( \$\{_fta_tmp_\[@\]\} \)
    return 0
}

#  Columnized print of an array of multi-field strings.
#  col_print <array_name> <min_space> <
#+ tab_stop [tab_stops]>
col_print() {
    [ $# -gt 2 ] || return 0
    local -a _cp_inp
    local -a _cp_spc
    local -a _cp_line
    local _cp_min
    local _cp_mcnt
    local _cp_pos
    local _cp_cnt
    local _cp_tab
    local -i _cp
    local -i _cpf
    local _cp_fld
    # WARNING: FOLLOWING LINE NOT BLANK -- IT IS QUOTED SPACES.
    local _cp_max='                                                            '
    set -f
    local IFS=${NO_WSP}
    eval _cp_inp=\(\ \$\{$1\[@\]\}\ \)
    [ ${#_cp_inp[@]} -gt 0 ] || return 0 # Empty is easy.
    _cp_mcnt=$2
    _cp_min=${_cp_max:1:${_cp_mcnt}}
    shift
    shift
    _cp_cnt=$#
    for (( _cp = 0 ; _cp < _cp_cnt ; _cp++ ))
    do
        _cp_spc[${#_cp_spc[@]}]="${_cp_max:2:$1}" #"
        shift
    done
    _cp_cnt=${#_cp_inp[@]}
    for (( _cp = 0 ; _cp < _cp_cnt ; _cp++ ))
    do
        _cp_pos=1
        IFS=${NO_WSP}$'\x20'
        _cp_line=( ${_cp_inp[${_cp}]} )
        IFS=${NO_WSP}
        for (( _cpf = 0 ; _cpf < ${#_cp_line[@]} ; _cpf++ ))
        do
            _cp_tab=${_cp_spc[${_cpf}]:${_cp_pos}}
            if [ ${#_cp_tab} -lt ${_cp_mcnt} ]
            then
                _cp_tab="${_cp_min}"
            fi
            echo -n "${_cp_tab}"
            (( _cp_pos = ${_cp_pos} + ${#_cp_tab} ))
            _cp_fld="${_cp_line[${_cpf}]}"
            echo -n ${_cp_fld}
            (( _cp_pos = ${_cp_pos} + ${#_cp_fld} ))
        done
        echo
    done
    set +f
    return 0
}

# # # # 'Hunt the Spammer' data flow # # # #

# Application return code
declare -i _hs_RC

# Original input, from which IP addresses are removed
# After which, domain names to check
declare -a uc_name

# Original input IP addresses are moved here
# After which, IP addresses to check
declare -a uc_address

# Names against which address expansion run
# Ready for name detail lookup
declare -a chk_name

# Addresses against which name expansion run
# Ready for address detail lookup
declare -a chk_address

#  Recursion is depth-first-by-name.
#  The expand_input_address maintains this list
#+ to prohibit looking up addresses twice during
#+ domain name recursion.
declare -a been_there_addr
been_there_addr=( '127.0.0.1' ) # Whitelist localhost

# Names which we have checked (or given up on)
declare -a known_name

# Addresses which we have checked (or given up on)
declare -a known_address

#  List of zero or more Blacklist servers to check.
#  Each 'known_address' will be checked against each server,
#+ with negative replies and failures suppressed.
declare -a list_server

# Indirection limit - set to zero == no limit
indirect=${SPAMMER_LIMIT:=2}

# # # # 'Hunt the Spammer' information output data # # # #

# Any domain name may have multiple IP addresses.
# Any IP address may have multiple domain names.
# Therefore, track unique address-name pairs.
declare -a known_pair
declare -a reverse_pair

#  In addition to the data flow variables; known_address
#+ known_name and list_server, the following are output to the
#+ external graphics interface file.

# Authority chain, parent -> SOA fields.
declare -a auth_chain

# Reference chain, parent name -> child name
declare -a ref_chain

# DNS chain - domain name -> address
declare -a name_address

# Name and service pairs - domain name -> service
declare -a name_srvc

# Name and resource pairs - domain name -> Resource Record
declare -a name_resource

# Parent and Child pairs - parent name -> child name
# This MAY NOT be the same as the ref_chain followed!
declare -a parent_child

# Address and Blacklist hit pairs - address->server
declare -a address_hits

# Dump interface file data
declare -f _dot_dump
_dot_dump=pend_dummy   # Initially a no-op

#  Data dump is enabled by setting the environment variable SPAMMER_DATA
#+ to the name of a writable file.
declare _dot_file

# Helper function for the dump-to-dot-file function
# dump_to_dot <array_name> <prefix>
dump_to_dot() {
    local -a _dda_tmp
    local -i _dda_cnt
    local _dda_form='    '${2}'%04u %s\n'
    local IFS=${NO_WSP}
    eval _dda_tmp=\(\ \$\{$1\[@\]\}\ \)
    _dda_cnt=${#_dda_tmp[@]}
    if [ ${_dda_cnt} -gt 0 ]
    then
        for (( _dda = 0 ; _dda < _dda_cnt ; _dda++ ))
        do
            printf "${_dda_form}" \
                   "${_dda}" "${_dda_tmp[${_dda}]}" >>${_dot_file}
        done
    fi
}

# Which will also set _dot_dump to this function . . .
dump_dot() {
    local -i _dd_cnt
    echo '# Data vintage: '$(date -R) >${_dot_file}
    echo '# ABS Guide: is_spammer.bash; v2, 2004-msz' >>${_dot_file}
    echo >>${_dot_file}
    echo 'digraph G {' >>${_dot_file}

    if [ ${#known_name[@]} -gt 0 ]
    then
        echo >>${_dot_file}
        echo '# Known domain name nodes' >>${_dot_file}
        _dd_cnt=${#known_name[@]}
        for (( _dd = 0 ; _dd < _dd_cnt ; _dd++ ))
        do
            printf '    N%04u [label="%s"] ;\n' \
                   "${_dd}" "${known_name[${_dd}]}" >>${_dot_file}
        done
    fi

    if [ ${#known_address[@]} -gt 0 ]
    then
        echo >>${_dot_file}
        echo '# Known address nodes' >>${_dot_file}
        _dd_cnt=${#known_address[@]}
        for (( _dd = 0 ; _dd < _dd_cnt ; _dd++ ))
        do
            printf '    A%04u [label="%s"] ;\n' \
                   "${_dd}" "${known_address[${_dd}]}" >>${_dot_file}
        done
    fi

    echo                                   >>${_dot_file}
    echo '/*'                              >>${_dot_file}
    echo ' * Known relationships :: User conversion to'  >>${_dot_file}
    echo ' * graphic form by hand or program required.'  >>${_dot_file}
    echo ' *'                              >>${_dot_file}

    if [ ${#auth_chain[@]} -gt 0 ]
    then
      echo >>${_dot_file}
      echo '# Authority ref. edges followed & field source.' >>${_dot_file}
        dump_to_dot auth_chain AC
    fi

    if [ ${#ref_chain[@]} -gt 0 ]
    then
        echo >>${_dot_file}
        echo '# Name ref. edges followed and field source.' >>${_dot_file}
        dump_to_dot ref_chain RC
    fi

    if [ ${#name_address[@]} -gt 0 ]
    then
        echo >>${_dot_file}
        echo '# Known name->address edges' >>${_dot_file}
        dump_to_dot name_address NA
    fi

    if [ ${#name_srvc[@]} -gt 0 ]
    then
        echo >>${_dot_file}
        echo '# Known name->service edges' >>${_dot_file}
        dump_to_dot name_srvc NS
    fi

    if [ ${#name_resource[@]} -gt 0 ]
    then
        echo >>${_dot_file}
        echo '# Known name->resource edges' >>${_dot_file}
        dump_to_dot name_resource NR
    fi

    if [ ${#parent_child[@]} -gt 0 ]
    then
        echo >>${_dot_file}
        echo '# Known parent->child edges' >>${_dot_file}
        dump_to_dot parent_child PC
    fi

    if [ ${#list_server[@]} -gt 0 ]
    then
        echo >>${_dot_file}
        echo '# Known Blacklist nodes' >>${_dot_file}
        _dd_cnt=${#list_server[@]}
        for (( _dd = 0 ; _dd < _dd_cnt ; _dd++ ))
        do
            printf '    LS%04u [label="%s"] ;\n' \
                   "${_dd}" "${list_server[${_dd}]}" >>${_dot_file}
        done
    fi

    unique_lines address_hits address_hits
    if [ ${#address_hits[@]} -gt 0 ]
    then
      echo >>${_dot_file}
      echo '# Known address->Blacklist_hit edges' >>${_dot_file}
      echo '# CAUTION: dig warnings can trigger false hits.' >>${_dot_file}
       dump_to_dot address_hits AH
    fi
    echo          >>${_dot_file}
    echo ' *'     >>${_dot_file}
    echo ' * That is a lot of relationships. Happy graphing.' >>${_dot_file}
    echo ' */'    >>${_dot_file}
    echo '}'      >>${_dot_file}
    return 0
}

# # # # 'Hunt the Spammer' execution flow # # # #

#  Execution trace is enabled by setting the
#+ environment variable SPAMMER_TRACE to the name of a writable file.
declare -a _trace_log
declare _log_file

# Function to fill the trace log
trace_logger() {
    _trace_log[${#_trace_log[@]}]=${_pend_current_}
}

# Dump trace log to file function variable.
declare -f _log_dump
_log_dump=pend_dummy   # Initially a no-op.

# Dump the trace log to a file.
dump_log() {
    local -i _dl_cnt
    _dl_cnt=${#_trace_log[@]}
    for (( _dl = 0 ; _dl < _dl_cnt ; _dl++ ))
    do
        echo ${_trace_log[${_dl}]} >> ${_log_file}
    done
    _dl_cnt=${#_pending_[@]}
    if [ ${_dl_cnt} -gt 0 ]
    then
        _dl_cnt=${_dl_cnt}-1
        echo '# # # Operations stack not empty # # #' >> ${_log_file}
        for (( _dl = ${_dl_cnt} ; _dl >= 0 ; _dl-- ))
        do
            echo ${_pending_[${_dl}]} >> ${_log_file}
        done
    fi
}

# # # Utility program 'dig' wrappers # # #
#
#  These wrappers are derived from the
#+ examples shown in dig_wrappers.bash.
#
#  The major difference is these return
#+ their results as a list in an array.
#
#  See dig_wrappers.bash for details and
#+ use that script to develop any changes.
#
# # #

# Short form answer: 'dig' parses answer.

# Forward lookup :: Name -> Address
# short_fwd <domain_name> <array_name>
short_fwd() {
    local -a _sf_reply
    local -i _sf_rc
    local -i _sf_cnt
    IFS=${NO_WSP}
echo -n '.'
# echo 'sfwd: '${1}
  _sf_reply=( $(dig +short ${1} -c in -t a 2>/dev/null) )
  _sf_rc=$?
  if [ ${_sf_rc} -ne 0 ]
  then
    _trace_log[${#_trace_log[@]}]='## Lookup error '${_sf_rc}' on '${1}' ##'
# [ ${_sf_rc} -ne 9 ] && pend_drop
        return ${_sf_rc}
    else
        # Some versions of 'dig' return warnings on stdout.
        _sf_cnt=${#_sf_reply[@]}
        for (( _sf = 0 ; _sf < ${_sf_cnt} ; _sf++ ))
        do
            [ 'x'${_sf_reply[${_sf}]:0:2} == 'x;;' ] &&
                unset _sf_reply[${_sf}]
        done
        eval $2=\( \$\{_sf_reply\[@\]\} \)
    fi
    return 0
}

# Reverse lookup :: Address -> Name
# short_rev <ip_address> <array_name>
short_rev() {
    local -a _sr_reply
    local -i _sr_rc
    local -i _sr_cnt
    IFS=${NO_WSP}
echo -n '.'
# echo 'srev: '${1}
  _sr_reply=( $(dig +short -x ${1} 2>/dev/null) )
  _sr_rc=$?
  if [ ${_sr_rc} -ne 0 ]
  then
    _trace_log[${#_trace_log[@]}]='## Lookup error '${_sr_rc}' on '${1}' ##'
# [ ${_sr_rc} -ne 9 ] && pend_drop
        return ${_sr_rc}
    else
        # Some versions of 'dig' return warnings on stdout.
        _sr_cnt=${#_sr_reply[@]}
        for (( _sr = 0 ; _sr < ${_sr_cnt} ; _sr++ ))
        do
            [ 'x'${_sr_reply[${_sr}]:0:2} == 'x;;' ] &&
                unset _sr_reply[${_sr}]
        done
        eval $2=\( \$\{_sr_reply\[@\]\} \)
    fi
    return 0
}

# Special format lookup used to query blacklist servers.
# short_text <ip_address> <array_name>
short_text() {
    local -a _st_reply
    local -i _st_rc
    local -i _st_cnt
    IFS=${NO_WSP}
# echo 'stxt: '${1}
  _st_reply=( $(dig +short ${1} -c in -t txt 2>/dev/null) )
  _st_rc=$?
  if [ ${_st_rc} -ne 0 ]
  then
    _trace_log[${#_trace_log[@]}]='##Text lookup error '${_st_rc}' on '${1}'##'
# [ ${_st_rc} -ne 9 ] && pend_drop
        return ${_st_rc}
    else
        # Some versions of 'dig' return warnings on stdout.
        _st_cnt=${#_st_reply[@]}
        for (( _st = 0 ; _st < ${#_st_cnt} ; _st++ ))
        do
            [ 'x'${_st_reply[${_st}]:0:2} == 'x;;' ] &&
                unset _st_reply[${_st}]
        done
        eval $2=\( \$\{_st_reply\[@\]\} \)
    fi
    return 0
}

# The long forms, a.k.a., the parse it yourself versions

# RFC 2782   Service lookups
# dig +noall +nofail +answer _ldap._tcp.openldap.org -t srv
# _<service>._<protocol>.<domain_name>
# _ldap._tcp.openldap.org. 3600   IN     SRV    0 0 389 ldap.openldap.org.
# domain TTL Class SRV Priority Weight Port Target

# Forward lookup :: Name -> poor man's zone transfer
# long_fwd <domain_name> <array_name>
long_fwd() {
    local -a _lf_reply
    local -i _lf_rc
    local -i _lf_cnt
    IFS=${NO_WSP}
echo -n ':'
# echo 'lfwd: '${1}
  _lf_reply=( $(
     dig +noall +nofail +answer +authority +additional \
         ${1} -t soa ${1} -t mx ${1} -t any 2>/dev/null) )
  _lf_rc=$?
  if [ ${_lf_rc} -ne 0 ]
  then
    _trace_log[${#_trace_log[@]}]='# Zone lookup err '${_lf_rc}' on '${1}' #'
# [ ${_lf_rc} -ne 9 ] && pend_drop
        return ${_lf_rc}
    else
        # Some versions of 'dig' return warnings on stdout.
        _lf_cnt=${#_lf_reply[@]}
        for (( _lf = 0 ; _lf < ${_lf_cnt} ; _lf++ ))
        do
            [ 'x'${_lf_reply[${_lf}]:0:2} == 'x;;' ] &&
                unset _lf_reply[${_lf}]
        done
        eval $2=\( \$\{_lf_reply\[@\]\} \)
    fi
    return 0
}
#  The reverse lookup domain name corresponding to the IPv6 address:
#      4321:0:1:2:3:4:567:89ab
#  would be (nibble, I.E: Hexdigit) reversed:
#  b.a.9.8.7.6.5.0.4.0.0.0.3.0.0.0.2.0.0.0.1.0.0.0.0.0.0.0.1.2.3.4.IP6.ARPA.

# Reverse lookup :: Address -> poor man's delegation chain
# long_rev <rev_ip_address> <array_name>
long_rev() {
    local -a _lr_reply
    local -i _lr_rc
    local -i _lr_cnt
    local _lr_dns
    _lr_dns=${1}'.in-addr.arpa.'
    IFS=${NO_WSP}
echo -n ':'
# echo 'lrev: '${1}
  _lr_reply=( $(
       dig +noall +nofail +answer +authority +additional \
           ${_lr_dns} -t soa ${_lr_dns} -t any 2>/dev/null) )
  _lr_rc=$?
  if [ ${_lr_rc} -ne 0 ]
  then
    _trace_log[${#_trace_log[@]}]='# Deleg lkp error '${_lr_rc}' on '${1}' #'
# [ ${_lr_rc} -ne 9 ] && pend_drop
        return ${_lr_rc}
    else
        # Some versions of 'dig' return warnings on stdout.
        _lr_cnt=${#_lr_reply[@]}
        for (( _lr = 0 ; _lr < ${_lr_cnt} ; _lr++ ))
        do
            [ 'x'${_lr_reply[${_lr}]:0:2} == 'x;;' ] &&
                unset _lr_reply[${_lr}]
        done
        eval $2=\( \$\{_lr_reply\[@\]\} \)
    fi
    return 0
}

# # # Application specific functions # # #

# Mung a possible name; suppresses root and TLDs.
# name_fixup <string>
name_fixup(){
    local -a _nf_tmp
    local -i _nf_end
    local _nf_str
    local IFS
    _nf_str=$(to_lower ${1})
    _nf_str=$(to_dot ${_nf_str})
    _nf_end=${#_nf_str}-1
    [ ${_nf_str:${_nf_end}} != '.' ] &&
        _nf_str=${_nf_str}'.'
    IFS=${ADR_IFS}
    _nf_tmp=( ${_nf_str} )
    IFS=${WSP_IFS}
    _nf_end=${#_nf_tmp[@]}
    case ${_nf_end} in
    0) # No dots, only dots.
        echo
        return 1
    ;;
    1) # Only a TLD.
        echo
        return 1
    ;;
    2) # Maybe okay.
       echo ${_nf_str}
       return 0
       # Needs a lookup table?
       if [ ${#_nf_tmp[1]} -eq 2 ]
       then # Country coded TLD.
           echo
           return 1
       else
           echo ${_nf_str}
           return 0
       fi
    ;;
    esac
    echo ${_nf_str}
    return 0
}

# Grope and mung original input(s).
split_input() {
    [ ${#uc_name[@]} -gt 0 ] || return 0
    local -i _si_cnt
    local -i _si_len
    local _si_str
    unique_lines uc_name uc_name
    _si_cnt=${#uc_name[@]}
    for (( _si = 0 ; _si < _si_cnt ; _si++ ))
    do
        _si_str=${uc_name[$_si]}
        if is_address ${_si_str}
        then
            uc_address[${#uc_address[@]}]=${_si_str}
            unset uc_name[$_si]
        else
            if ! uc_name[$_si]=$(name_fixup ${_si_str})
            then
                unset ucname[$_si]
            fi
        fi
    done
  uc_name=( ${uc_name[@]} )
  _si_cnt=${#uc_name[@]}
  _trace_log[${#_trace_log[@]}]='#Input '${_si_cnt}' unchkd name input(s).#'
  _si_cnt=${#uc_address[@]}
  _trace_log[${#_trace_log[@]}]='#Input '${_si_cnt}' unchkd addr input(s).#'
    return 0
}

# # # Discovery functions -- recursively interlocked by external data # # #
# # # The leading 'if list is empty; return 0' in each is required. # # #

# Recursion limiter
# limit_chk() <next_level>
limit_chk() {
    local -i _lc_lmt
    # Check indirection limit.
    if [ ${indirect} -eq 0 ] || [ $# -eq 0 ]
    then
        # The 'do-forever' choice
        echo 1                 # Any value will do.
        return 0               # OK to continue.
    else
        # Limiting is in effect.
        if [ ${indirect} -lt ${1} ]
        then
            echo ${1}          # Whatever.
            return 1           # Stop here.
        else
            _lc_lmt=${1}+1     # Bump the given limit.
            echo ${_lc_lmt}    # Echo it.
            return 0           # OK to continue.
        fi
    fi
}

# For each name in uc_name:
#     Move name to chk_name.
#     Add addresses to uc_address.
#     Pend expand_input_address.
#     Repeat until nothing new found.
# expand_input_name <indirection_limit>
expand_input_name() {
    [ ${#uc_name[@]} -gt 0 ] || return 0
    local -a _ein_addr
    local -a _ein_new
    local -i _ucn_cnt
    local -i _ein_cnt
    local _ein_tst
    _ucn_cnt=${#uc_name[@]}

    if  ! _ein_cnt=$(limit_chk ${1})
    then
        return 0
    fi

    for (( _ein = 0 ; _ein < _ucn_cnt ; _ein++ ))
    do
        if short_fwd ${uc_name[${_ein}]} _ein_new
        then
          for (( _ein_cnt = 0 ; _ein_cnt < ${#_ein_new[@]}; _ein_cnt++ ))
          do
              _ein_tst=${_ein_new[${_ein_cnt}]}
              if is_address ${_ein_tst}
              then
                  _ein_addr[${#_ein_addr[@]}]=${_ein_tst}
              fi
    done
        fi
    done
    unique_lines _ein_addr _ein_addr     # Scrub duplicates.
    edit_exact chk_address _ein_addr     # Scrub pending detail.
    edit_exact known_address _ein_addr   # Scrub already detailed.
 if [ ${#_ein_addr[@]} -gt 0 ]        # Anything new?
 then
   uc_address=( ${uc_address[@]} ${_ein_addr[@]} )
   pend_func expand_input_address ${1}
   _trace_log[${#_trace_log[@]}]='#Add '${#_ein_addr[@]}' unchkd addr inp.#'
    fi
    edit_exact chk_name uc_name          # Scrub pending detail.
    edit_exact known_name uc_name        # Scrub already detailed.
    if [ ${#uc_name[@]} -gt 0 ]
    then
        chk_name=( ${chk_name[@]} ${uc_name[@]}  )
        pend_func detail_each_name ${1}
    fi
    unset uc_name[@]
    return 0
}

# For each address in uc_address:
#     Move address to chk_address.
#     Add names to uc_name.
#     Pend expand_input_name.
#     Repeat until nothing new found.
# expand_input_address <indirection_limit>
expand_input_address() {
    [ ${#uc_address[@]} -gt 0 ] || return 0
    local -a _eia_addr
    local -a _eia_name
    local -a _eia_new
    local -i _uca_cnt
    local -i _eia_cnt
    local _eia_tst
    unique_lines uc_address _eia_addr
    unset uc_address[@]
    edit_exact been_there_addr _eia_addr
    _uca_cnt=${#_eia_addr[@]}
    [ ${_uca_cnt} -gt 0 ] &&
        been_there_addr=( ${been_there_addr[@]} ${_eia_addr[@]} )

    for (( _eia = 0 ; _eia < _uca_cnt ; _eia++ ))
     do
       if short_rev ${_eia_addr[${_eia}]} _eia_new
       then
         for (( _eia_cnt = 0 ; _eia_cnt < ${#_eia_new[@]} ; _eia_cnt++ ))
         do
           _eia_tst=${_eia_new[${_eia_cnt}]}
           if _eia_tst=$(name_fixup ${_eia_tst})
           then
             _eia_name[${#_eia_name[@]}]=${_eia_tst}
       fi
     done
           fi
    done
    unique_lines _eia_name _eia_name     # Scrub duplicates.
    edit_exact chk_name _eia_name        # Scrub pending detail.
    edit_exact known_name _eia_name      # Scrub already detailed.
 if [ ${#_eia_name[@]} -gt 0 ]        # Anything new?
 then
   uc_name=( ${uc_name[@]} ${_eia_name[@]} )
   pend_func expand_input_name ${1}
   _trace_log[${#_trace_log[@]}]='#Add '${#_eia_name[@]}' unchkd name inp.#'
    fi
    edit_exact chk_address _eia_addr     # Scrub pending detail.
    edit_exact known_address _eia_addr   # Scrub already detailed.
    if [ ${#_eia_addr[@]} -gt 0 ]        # Anything new?
    then
        chk_address=( ${chk_address[@]} ${_eia_addr[@]} )
        pend_func detail_each_address ${1}
    fi
    return 0
}

# The parse-it-yourself zone reply.
# The input is the chk_name list.
# detail_each_name <indirection_limit>
detail_each_name() {
    [ ${#chk_name[@]} -gt 0 ] || return 0
    local -a _den_chk       # Names to check
    local -a _den_name      # Names found here
    local -a _den_address   # Addresses found here
    local -a _den_pair      # Pairs found here
    local -a _den_rev       # Reverse pairs found here
    local -a _den_tmp       # Line being parsed
    local -a _den_auth      # SOA contact being parsed
    local -a _den_new       # The zone reply
    local -a _den_pc        # Parent-Child gets big fast
    local -a _den_ref       # So does reference chain
    local -a _den_nr        # Name-Resource can be big
    local -a _den_na        # Name-Address
    local -a _den_ns        # Name-Service
    local -a _den_achn      # Chain of Authority
    local -i _den_cnt       # Count of names to detail
    local -i _den_lmt       # Indirection limit
    local _den_who          # Named being processed
    local _den_rec          # Record type being processed
    local _den_cont         # Contact domain
    local _den_str          # Fixed up name string
    local _den_str2         # Fixed up reverse
    local IFS=${WSP_IFS}

    # Local, unique copy of names to check
    unique_lines chk_name _den_chk
    unset chk_name[@]       # Done with globals.

    # Less any names already known
    edit_exact known_name _den_chk
    _den_cnt=${#_den_chk[@]}

    # If anything left, add to known_name.
    [ ${_den_cnt} -gt 0 ] &&
        known_name=( ${known_name[@]} ${_den_chk[@]} )

    # for the list of (previously) unknown names . . .
    for (( _den = 0 ; _den < _den_cnt ; _den++ ))
    do
        _den_who=${_den_chk[${_den}]}
        if long_fwd ${_den_who} _den_new
        then
            unique_lines _den_new _den_new
            if [ ${#_den_new[@]} -eq 0 ]
            then
                _den_pair[${#_den_pair[@]}]='0.0.0.0 '${_den_who}
            fi

            # Parse each line in the reply.
            for (( _line = 0 ; _line < ${#_den_new[@]} ; _line++ ))
            do
                IFS=${NO_WSP}$'\x09'$'\x20'
                _den_tmp=( ${_den_new[${_line}]} )
                IFS=${WSP_IFS}
              # If usable record and not a warning message . . .
              if [ ${#_den_tmp[@]} -gt 4 ] && [ 'x'${_den_tmp[0]} != 'x;;' ]
              then
                    _den_rec=${_den_tmp[3]}
                    _den_nr[${#_den_nr[@]}]=${_den_who}' '${_den_rec}
                    # Begin at RFC1033 (+++)
                    case ${_den_rec} in

#<name> [<ttl>]  [<class>] SOA <origin> <person>
                    SOA) # Start Of Authority
    if _den_str=$(name_fixup ${_den_tmp[0]})
    then
      _den_name[${#_den_name[@]}]=${_den_str}
      _den_achn[${#_den_achn[@]}]=${_den_who}' '${_den_str}' SOA'
      # SOA origin -- domain name of master zone record
      if _den_str2=$(name_fixup ${_den_tmp[4]})
      then
        _den_name[${#_den_name[@]}]=${_den_str2}
        _den_achn[${#_den_achn[@]}]=${_den_who}' '${_den_str2}' SOA.O'
      fi
      # Responsible party e-mail address (possibly bogus).
      # Possibility of first.last@domain.name ignored.
      set -f
      if _den_str2=$(name_fixup ${_den_tmp[5]})
      then
        IFS=${ADR_IFS}
        _den_auth=( ${_den_str2} )
        IFS=${WSP_IFS}
        if [ ${#_den_auth[@]} -gt 2 ]
        then
          _den_cont=${_den_auth[1]}
          for (( _auth = 2 ; _auth < ${#_den_auth[@]} ; _auth++ ))
          do
            _den_cont=${_den_cont}'.'${_den_auth[${_auth}]}
          done
          _den_name[${#_den_name[@]}]=${_den_cont}'.'
          _den_achn[${#_den_achn[@]}]=${_den_who}' '${_den_cont}'. SOA.C'
                                fi
        fi
        set +f
                        fi
                    ;;


      A) # IP(v4) Address Record
      if _den_str=$(name_fixup ${_den_tmp[0]})
      then
        _den_name[${#_den_name[@]}]=${_den_str}
        _den_pair[${#_den_pair[@]}]=${_den_tmp[4]}' '${_den_str}
        _den_na[${#_den_na[@]}]=${_den_str}' '${_den_tmp[4]}
        _den_ref[${#_den_ref[@]}]=${_den_who}' '${_den_str}' A'
      else
        _den_pair[${#_den_pair[@]}]=${_den_tmp[4]}' unknown.domain'
        _den_na[${#_den_na[@]}]='unknown.domain '${_den_tmp[4]}
        _den_ref[${#_den_ref[@]}]=${_den_who}' unknown.domain A'
      fi
      _den_address[${#_den_address[@]}]=${_den_tmp[4]}
      _den_pc[${#_den_pc[@]}]=${_den_who}' '${_den_tmp[4]}
             ;;

             NS) # Name Server Record
             # Domain name being serviced (may be other than current)
               if _den_str=$(name_fixup ${_den_tmp[0]})
                 then
                   _den_name[${#_den_name[@]}]=${_den_str}
                   _den_ref[${#_den_ref[@]}]=${_den_who}' '${_den_str}' NS'

             # Domain name of service provider
             if _den_str2=$(name_fixup ${_den_tmp[4]})
             then
               _den_name[${#_den_name[@]}]=${_den_str2}
               _den_ref[${#_den_ref[@]}]=${_den_who}' '${_den_str2}' NSH'
               _den_ns[${#_den_ns[@]}]=${_den_str2}' NS'
               _den_pc[${#_den_pc[@]}]=${_den_str}' '${_den_str2}
              fi
               fi
                    ;;

             MX) # Mail Server Record
                 # Domain name being serviced (wildcards not handled here)
             if _den_str=$(name_fixup ${_den_tmp[0]})
             then
               _den_name[${#_den_name[@]}]=${_den_str}
               _den_ref[${#_den_ref[@]}]=${_den_who}' '${_den_str}' MX'
             fi
             # Domain name of service provider
             if _den_str=$(name_fixup ${_den_tmp[5]})
             then
               _den_name[${#_den_name[@]}]=${_den_str}
               _den_ref[${#_den_ref[@]}]=${_den_who}' '${_den_str}' MXH'
               _den_ns[${#_den_ns[@]}]=${_den_str}' MX'
               _den_pc[${#_den_pc[@]}]=${_den_who}' '${_den_str}
             fi
                    ;;

             PTR) # Reverse address record
                  # Special name
             if _den_str=$(name_fixup ${_den_tmp[0]})
             then
               _den_ref[${#_den_ref[@]}]=${_den_who}' '${_den_str}' PTR'
               # Host name (not a CNAME)
               if _den_str2=$(name_fixup ${_den_tmp[4]})
               then
                 _den_rev[${#_den_rev[@]}]=${_den_str}' '${_den_str2}
                 _den_ref[${#_den_ref[@]}]=${_den_who}' '${_den_str2}' PTRH'
                 _den_pc[${#_den_pc[@]}]=${_den_who}' '${_den_str}
               fi
             fi
                    ;;

             AAAA) # IP(v6) Address Record
             if _den_str=$(name_fixup ${_den_tmp[0]})
             then
               _den_name[${#_den_name[@]}]=${_den_str}
               _den_pair[${#_den_pair[@]}]=${_den_tmp[4]}' '${_den_str}
               _den_na[${#_den_na[@]}]=${_den_str}' '${_den_tmp[4]}
               _den_ref[${#_den_ref[@]}]=${_den_who}' '${_den_str}' AAAA'
               else
                 _den_pair[${#_den_pair[@]}]=${_den_tmp[4]}' unknown.domain'
                 _den_na[${#_den_na[@]}]='unknown.domain '${_den_tmp[4]}
                 _den_ref[${#_den_ref[@]}]=${_den_who}' unknown.domain'
               fi
               # No processing for IPv6 addresses
               _den_pc[${#_den_pc[@]}]=${_den_who}' '${_den_tmp[4]}
                    ;;

             CNAME) # Alias name record
                    # Nickname
             if _den_str=$(name_fixup ${_den_tmp[0]})
             then
               _den_name[${#_den_name[@]}]=${_den_str}
               _den_ref[${#_den_ref[@]}]=${_den_who}' '${_den_str}' CNAME'
               _den_pc[${#_den_pc[@]}]=${_den_who}' '${_den_str}
             fi
                    # Hostname
             if _den_str=$(name_fixup ${_den_tmp[4]})
             then
               _den_name[${#_den_name[@]}]=${_den_str}
               _den_ref[${#_den_ref[@]}]=${_den_who}' '${_den_str}' CHOST'
               _den_pc[${#_den_pc[@]}]=${_den_who}' '${_den_str}
             fi
                    ;;
#            TXT)
#            ;;
                    esac
                fi
            done
        else # Lookup error == 'A' record 'unknown address'
            _den_pair[${#_den_pair[@]}]='0.0.0.0 '${_den_who}
        fi
    done

    # Control dot array growth.
    unique_lines _den_achn _den_achn      # Works best, all the same.
    edit_exact auth_chain _den_achn       # Works best, unique items.
    if [ ${#_den_achn[@]} -gt 0 ]
    then
        IFS=${NO_WSP}
        auth_chain=( ${auth_chain[@]} ${_den_achn[@]} )
        IFS=${WSP_IFS}
    fi

    unique_lines _den_ref _den_ref      # Works best, all the same.
    edit_exact ref_chain _den_ref       # Works best, unique items.
    if [ ${#_den_ref[@]} -gt 0 ]
    then
        IFS=${NO_WSP}
        ref_chain=( ${ref_chain[@]} ${_den_ref[@]} )
        IFS=${WSP_IFS}
    fi

    unique_lines _den_na _den_na
    edit_exact name_address _den_na
    if [ ${#_den_na[@]} -gt 0 ]
    then
        IFS=${NO_WSP}
        name_address=( ${name_address[@]} ${_den_na[@]} )
        IFS=${WSP_IFS}
    fi

    unique_lines _den_ns _den_ns
    edit_exact name_srvc _den_ns
    if [ ${#_den_ns[@]} -gt 0 ]
    then
        IFS=${NO_WSP}
        name_srvc=( ${name_srvc[@]} ${_den_ns[@]} )
        IFS=${WSP_IFS}
    fi

    unique_lines _den_nr _den_nr
    edit_exact name_resource _den_nr
    if [ ${#_den_nr[@]} -gt 0 ]
    then
        IFS=${NO_WSP}
        name_resource=( ${name_resource[@]} ${_den_nr[@]} )
        IFS=${WSP_IFS}
    fi

    unique_lines _den_pc _den_pc
    edit_exact parent_child _den_pc
    if [ ${#_den_pc[@]} -gt 0 ]
    then
        IFS=${NO_WSP}
        parent_child=( ${parent_child[@]} ${_den_pc[@]} )
        IFS=${WSP_IFS}
    fi

    # Update list known_pair (Address and Name).
    unique_lines _den_pair _den_pair
    edit_exact known_pair _den_pair
    if [ ${#_den_pair[@]} -gt 0 ]  # Anything new?
    then
        IFS=${NO_WSP}
        known_pair=( ${known_pair[@]} ${_den_pair[@]} )
        IFS=${WSP_IFS}
    fi

    # Update list of reverse pairs.
    unique_lines _den_rev _den_rev
    edit_exact reverse_pair _den_rev
    if [ ${#_den_rev[@]} -gt 0 ]   # Anything new?
    then
        IFS=${NO_WSP}
        reverse_pair=( ${reverse_pair[@]} ${_den_rev[@]} )
        IFS=${WSP_IFS}
    fi

    # Check indirection limit -- give up if reached.
    if ! _den_lmt=$(limit_chk ${1})
    then
        return 0
    fi

# Execution engine is LIFO. Order of pend operations is important.
# Did we define any new addresses?
unique_lines _den_address _den_address    # Scrub duplicates.
edit_exact known_address _den_address     # Scrub already processed.
edit_exact un_address _den_address        # Scrub already waiting.
if [ ${#_den_address[@]} -gt 0 ]          # Anything new?
then
  uc_address=( ${uc_address[@]} ${_den_address[@]} )
  pend_func expand_input_address ${_den_lmt}
  _trace_log[${#_trace_log[@]}]='# Add '${#_den_address[@]}' unchkd addr. #'
    fi

# Did we find any new names?
unique_lines _den_name _den_name          # Scrub duplicates.
edit_exact known_name _den_name           # Scrub already processed.
edit_exact uc_name _den_name              # Scrub already waiting.
if [ ${#_den_name[@]} -gt 0 ]             # Anything new?
then
  uc_name=( ${uc_name[@]} ${_den_name[@]} )
  pend_func expand_input_name ${_den_lmt}
  _trace_log[${#_trace_log[@]}]='#Added '${#_den_name[@]}' unchkd name#'
    fi
    return 0
}

# The parse-it-yourself delegation reply
# Input is the chk_address list.
# detail_each_address <indirection_limit>
detail_each_address() {
    [ ${#chk_address[@]} -gt 0 ] || return 0
    unique_lines chk_address chk_address
    edit_exact known_address chk_address
    if [ ${#chk_address[@]} -gt 0 ]
    then
        known_address=( ${known_address[@]} ${chk_address[@]} )
        unset chk_address[@]
    fi
    return 0
}

# # # Application specific output functions # # #

# Pretty print the known pairs.
report_pairs() {
    echo
    echo 'Known network pairs.'
    col_print known_pair 2 5 30

    if [ ${#auth_chain[@]} -gt 0 ]
    then
        echo
        echo 'Known chain of authority.'
        col_print auth_chain 2 5 30 55
    fi

    if [ ${#reverse_pair[@]} -gt 0 ]
    then
        echo
        echo 'Known reverse pairs.'
        col_print reverse_pair 2 5 55
    fi
    return 0
}

# Check an address against the list of blacklist servers.
# A good place to capture for GraphViz: address->status(server(reports))
# check_lists <ip_address>
check_lists() {
    [ $# -eq 1 ] || return 1
    local -a _cl_fwd_addr
    local -a _cl_rev_addr
    local -a _cl_reply
    local -i _cl_rc
    local -i _ls_cnt
    local _cl_dns_addr
    local _cl_lkup

    split_ip ${1} _cl_fwd_addr _cl_rev_addr
    _cl_dns_addr=$(dot_array _cl_rev_addr)'.'
    _ls_cnt=${#list_server[@]}
    echo '    Checking address '${1}
    for (( _cl = 0 ; _cl < _ls_cnt ; _cl++ ))
    do
      _cl_lkup=${_cl_dns_addr}${list_server[${_cl}]}
      if short_text ${_cl_lkup} _cl_reply
      then
        if [ ${#_cl_reply[@]} -gt 0 ]
        then
          echo '        Records from '${list_server[${_cl}]}
          address_hits[${#address_hits[@]}]=${1}' '${list_server[${_cl}]}
          _hs_RC=2
          for (( _clr = 0 ; _clr < ${#_cl_reply[@]} ; _clr++ ))
          do
            echo '            '${_cl_reply[${_clr}]}
          done
        fi
      fi
    done
    return 0
}

# # # The usual application glue # # #

# Who did it?
credits() {
   echo
   echo 'Advanced Bash Scripting Guide: is_spammer.bash, v2, 2004-msz'
}

# How to use it?
# (See also, "Quickstart" at end of script.)
usage() {
    cat <<-'_usage_statement_'
    The script is_spammer.bash requires either one or two arguments.

    arg 1) May be one of:
        a) A domain name
        b) An IPv4 address
        c) The name of a file with any mix of names
           and addresses, one per line.

    arg 2) May be one of:
        a) A Blacklist server domain name
        b) The name of a file with Blacklist server
           domain names, one per line.
        c) If not present, a default list of (free)
           Blacklist servers is used.
        d) If a filename of an empty, readable, file
           is given,
           Blacklist server lookup is disabled.

    All script output is written to stdout.

    Return codes: 0 -> All OK, 1 -> Script failure,
                  2 -> Something is Blacklisted.

    Requires the external program 'dig' from the 'bind-9'
    set of DNS programs.  See: http://www.isc.org

    The domain name lookup depth limit defaults to 2 levels.
    Set the environment variable SPAMMER_LIMIT to change.
    SPAMMER_LIMIT=0 means 'unlimited'

    Limit may also be set on the command-line.
    If arg#1 is an integer, the limit is set to that value
    and then the above argument rules are applied.

    Setting the environment variable 'SPAMMER_DATA' to a filename
    will cause the script to write a GraphViz graphic file.

    For the development version;
    Setting the environment variable 'SPAMMER_TRACE' to a filename
    will cause the execution engine to log a function call trace.

_usage_statement_
}

# The default list of Blacklist servers:
# Many choices, see: http://www.spews.org/lists.html

declare -a default_servers
# See: http://www.spamhaus.org (Conservative, well maintained)
default_servers[0]='sbl-xbl.spamhaus.org'
# See: http://ordb.org (Open mail relays)
default_servers[1]='relays.ordb.org'
# See: http://www.spamcop.net/ (You can report spammers here)
default_servers[2]='bl.spamcop.net'
# See: http://www.spews.org (An 'early detect' system)
default_servers[3]='l2.spews.dnsbl.sorbs.net'
# See: http://www.dnsbl.us.sorbs.net/using.shtml
default_servers[4]='dnsbl.sorbs.net'
# See: http://dsbl.org/usage (Various mail relay lists)
default_servers[5]='list.dsbl.org'
default_servers[6]='multihop.dsbl.org'
default_servers[7]='unconfirmed.dsbl.org'

# User input argument #1
setup_input() {
    if [ -e ${1} ] && [ -r ${1} ]  # Name of readable file
    then
        file_to_array ${1} uc_name
        echo 'Using filename >'${1}'< as input.'
    else
        if is_address ${1}          # IP address?
        then
            uc_address=( ${1} )
            echo 'Starting with address >'${1}'<'
        else                       # Must be a name.
            uc_name=( ${1} )
            echo 'Starting with domain name >'${1}'<'
        fi
    fi
    return 0
}

# User input argument #2
setup_servers() {
    if [ -e ${1} ] && [ -r ${1} ]  # Name of a readable file
    then
        file_to_array ${1} list_server
        echo 'Using filename >'${1}'< as blacklist server list.'
    else
        list_server=( ${1} )
        echo 'Using blacklist server >'${1}'<'
    fi
    return 0
}

# User environment variable SPAMMER_TRACE
live_log_die() {
    if [ ${SPAMMER_TRACE:=} ]    # Wants trace log?
    then
        if [ ! -e ${SPAMMER_TRACE} ]
        then
            if ! touch ${SPAMMER_TRACE} 2>/dev/null
            then
                pend_func echo $(printf '%q\n' \
                'Unable to create log file >'${SPAMMER_TRACE}'<')
                pend_release
                exit 1
            fi
            _log_file=${SPAMMER_TRACE}
            _pend_hook_=trace_logger
            _log_dump=dump_log
        else
            if [ ! -w ${SPAMMER_TRACE} ]
            then
                pend_func echo $(printf '%q\n' \
                'Unable to write log file >'${SPAMMER_TRACE}'<')
                pend_release
                exit 1
            fi
            _log_file=${SPAMMER_TRACE}
            echo '' > ${_log_file}
            _pend_hook_=trace_logger
            _log_dump=dump_log
        fi
    fi
    return 0
}

# User environment variable SPAMMER_DATA
data_capture() {
    if [ ${SPAMMER_DATA:=} ]    # Wants a data dump?
    then
        if [ ! -e ${SPAMMER_DATA} ]
        then
            if ! touch ${SPAMMER_DATA} 2>/dev/null
            then
                pend_func echo $(printf '%q]n' \
                'Unable to create data output file >'${SPAMMER_DATA}'<')
                pend_release
                exit 1
            fi
            _dot_file=${SPAMMER_DATA}
            _dot_dump=dump_dot
        else
            if [ ! -w ${SPAMMER_DATA} ]
            then
                pend_func echo $(printf '%q\n' \
                'Unable to write data output file >'${SPAMMER_DATA}'<')
                pend_release
                exit 1
            fi
            _dot_file=${SPAMMER_DATA}
            _dot_dump=dump_dot
        fi
    fi
    return 0
}

# Grope user specified arguments.
do_user_args() {
    if [ $# -gt 0 ] && is_number $1
    then
        indirect=$1
        shift
    fi

    case $# in                     # Did user treat us well?
        1)
            if ! setup_input $1    # Needs error checking.
            then
                pend_release
                $_log_dump
                exit 1
            fi
            list_server=( ${default_servers[@]} )
            _list_cnt=${#list_server[@]}
            echo 'Using default blacklist server list.'
            echo 'Search depth limit: '${indirect}
            ;;
        2)
            if ! setup_input $1    # Needs error checking.
            then
                pend_release
                $_log_dump
                exit 1
            fi
            if ! setup_servers $2  # Needs error checking.
            then
                pend_release
                $_log_dump
                exit 1
            fi
            echo 'Search depth limit: '${indirect}
            ;;
        *)
            pend_func usage
            pend_release
            $_log_dump
            exit 1
            ;;
    esac
    return 0
}

# A general purpose debug tool.
# list_array <array_name>
list_array() {
    [ $# -eq 1 ] || return 1  # One argument required.

    local -a _la_lines
    set -f
    local IFS=${NO_WSP}
    eval _la_lines=\(\ \$\{$1\[@\]\}\ \)
    echo
    echo "Element count "${#_la_lines[@]}" array "${1}
    local _ln_cnt=${#_la_lines[@]}

    for (( _i = 0; _i < ${_ln_cnt}; _i++ ))
    do
        echo 'Element '$_i' >'${_la_lines[$_i]}'<'
    done
    set +f
    return 0
}

# # # 'Hunt the Spammer' program code # # #
pend_init                               # Ready stack engine.
pend_func credits                       # Last thing to print.

# # # Deal with user # # #
live_log_die                            # Setup debug trace log.
data_capture                            # Setup data capture file.
echo
do_user_args $@

# # # Haven't exited yet - There is some hope # # #
# Discovery group - Execution engine is LIFO - pend
# in reverse order of execution.
_hs_RC=0                                # Hunt the Spammer return code
pend_mark
    pend_func report_pairs              # Report name-address pairs.

    # The two detail_* are mutually recursive functions.
    # They also pend expand_* functions as required.
    # These two (the last of ???) exit the recursion.
    pend_func detail_each_address       # Get all resources of addresses.
    pend_func detail_each_name          # Get all resources of names.

    #  The two expand_* are mutually recursive functions,
    #+ which pend additional detail_* functions as required.
    pend_func expand_input_address 1    # Expand input names by address.
    pend_func expand_input_name 1       # #xpand input addresses by name.

    # Start with a unique set of names and addresses.
    pend_func unique_lines uc_address uc_address
    pend_func unique_lines uc_name uc_name

    # Separate mixed input of names and addresses.
    pend_func split_input
pend_release

# # # Pairs reported -- Unique list of IP addresses found
echo
_ip_cnt=${#known_address[@]}
if [ ${#list_server[@]} -eq 0 ]
then
    echo 'Blacklist server list empty, none checked.'
else
    if [ ${_ip_cnt} -eq 0 ]
    then
        echo 'Known address list empty, none checked.'
    else
        _ip_cnt=${_ip_cnt}-1   # Start at top.
        echo 'Checking Blacklist servers.'
        for (( _ip = _ip_cnt ; _ip >= 0 ; _ip-- ))
        do
          pend_func check_lists $( printf '%q\n' ${known_address[$_ip]} )
        done
    fi
fi
pend_release
$_dot_dump                   # Graphics file dump
$_log_dump                   # Execution trace
echo


##############################
# Example output from script #
##############################
:<<-'_is_spammer_outputs_'

./is_spammer.bash 0 web4.alojamentos7.com

Starting with domain name >web4.alojamentos7.com<
Using default blacklist server list.
Search depth limit: 0
.:....::::...:::...:::.......::..::...:::.......::
Known network pairs.
    66.98.208.97             web4.alojamentos7.com.
    66.98.208.97             ns1.alojamentos7.com.
    69.56.202.147            ns2.alojamentos.ws.
    66.98.208.97             alojamentos7.com.
    66.98.208.97             web.alojamentos7.com.
    69.56.202.146            ns1.alojamentos.ws.
    69.56.202.146            alojamentos.ws.
    66.235.180.113           ns1.alojamentos.org.
    66.235.181.192           ns2.alojamentos.org.
    66.235.180.113           alojamentos.org.
    66.235.180.113           web6.alojamentos.org.
    216.234.234.30           ns1.theplanet.com.
    12.96.160.115            ns2.theplanet.com.
    216.185.111.52           mail1.theplanet.com.
    69.56.141.4              spooling.theplanet.com.
    216.185.111.40           theplanet.com.
    216.185.111.40           www.theplanet.com.
    216.185.111.52           mail.theplanet.com.

Checking Blacklist servers.
  Checking address 66.98.208.97
      Records from dnsbl.sorbs.net
  "Spam Received See: http://www.dnsbl.sorbs.net/lookup.shtml?66.98.208.97"
    Checking address 69.56.202.147
    Checking address 69.56.202.146
    Checking address 66.235.180.113
    Checking address 66.235.181.192
    Checking address 216.185.111.40
    Checking address 216.234.234.30
    Checking address 12.96.160.115
    Checking address 216.185.111.52
    Checking address 69.56.141.4

Advanced Bash Scripting Guide: is_spammer.bash, v2, 2004-msz

_is_spammer_outputs_

exit ${_hs_RC}

####################################################
#  The script ignores everything from here on down #
#+ because of the 'exit' command, just above.      #
####################################################



Quickstart
==========

 Prerequisites

  Bash version 2.05b or 3.00 (bash --version)
  A version of Bash which supports arrays. Array 
  support is included by default Bash configurations.

  'dig,' version 9.x.x (dig $HOSTNAME, see first line of output)
  A version of dig which supports the +short options. 
  See: dig_wrappers.bash for details.


 Optional Prerequisites

  'named,' a local DNS caching program. Any flavor will do.
  Do twice: dig $HOSTNAME 
  Check near bottom of output for: SERVER: 127.0.0.1#53
  That means you have one running.


 Optional Graphics Support

  'date,' a standard *nix thing. (date -R)

  dot Program to convert graphic description file to a 
  diagram. (dot -V)
  A part of the Graph-Viz set of programs.
  See: [http://www.research.att.com/sw/tools/graphviz||GraphViz]

  'dotty,' a visual editor for graphic description files.
  Also a part of the Graph-Viz set of programs.




 Quick Start

In the same directory as the is_spammer.bash script; 
Do: ./is_spammer.bash

 Usage Details

1. Blacklist server choices.

  (a) To use default, built-in list: Do nothing.

  (b) To use your own list: 

    i. Create a file with a single Blacklist server 
       domain name per line.

    ii. Provide that filename as the last argument to 
        the script.

  (c) To use a single Blacklist server: Last argument 
      to the script.

  (d) To disable Blacklist lookups:

    i. Create an empty file (touch spammer.nul)
       Your choice of filename.

    ii. Provide the filename of that empty file as the 
        last argument to the script.

2. Search depth limit.

  (a) To use the default value of 2: Do nothing.

  (b) To set a different limit: 
      A limit of 0 means: no limit.

    i. export SPAMMER_LIMIT=1
       or whatever limit you want.

    ii. OR provide the desired limit as the first 
       argument to the script.

3. Optional execution trace log.

  (a) To use the default setting of no log output: Do nothing.

  (b) To write an execution trace log:
      export SPAMMER_TRACE=spammer.log
      or whatever filename you want.

4. Optional graphic description file.

  (a) To use the default setting of no graphic file: Do nothing.

  (b) To write a Graph-Viz graphic description file:
      export SPAMMER_DATA=spammer.dot
      or whatever filename you want.

5. Where to start the search.

  (a) Starting with a single domain name:

    i. Without a command-line search limit: First 
       argument to script.

    ii. With a command-line search limit: Second 
        argument to script.

  (b) Starting with a single IP address:

    i. Without a command-line search limit: First 
       argument to script.

    ii. With a command-line search limit: Second 
        argument to script.

  (c) Starting with (mixed) multiple name(s) and/or address(es):
      Create a file with one name or address per line.
      Your choice of filename.

    i. Without a command-line search limit: Filename as 
       first argument to script.

    ii. With a command-line search limit: Filename as 
        second argument to script.

6. What to do with the display output.

  (a) To view display output on screen: Do nothing.

  (b) To save display output to a file: Redirect stdout to a filename.

  (c) To discard display output: Redirect stdout to /dev/null.

7. Temporary end of decision making. 
   press RETURN 
   wait (optionally, watch the dots and colons).

8. Optionally check the return code.

  (a) Return code 0: All OK

  (b) Return code 1: Script setup failure

  (c) Return code 2: Something was blacklisted.

9. Where is my graph (diagram)?

The script does not directly produce a graph (diagram). 
It only produces a graphic description file. You can 
process the graphic descriptor file that was output 
with the 'dot' program.

Until you edit that descriptor file, to describe the 
relationships you want shown, all that you will get is 
a bunch of labeled name and address nodes.

All of the script's discovered relationships are within 
a comment block in the graphic descriptor file, each 
with a descriptive heading.

The editing required to draw a line between a pair of 
nodes from the information in the descriptor file may 
be done with a text editor. 

Given these lines somewhere in the descriptor file:

# Known domain name nodes

N0000 [label="guardproof.info."] ;

N0002 [label="third.guardproof.info."] ;



# Known address nodes

A0000 [label="61.141.32.197"] ;



/*

# Known name->address edges

NA0000 third.guardproof.info. 61.141.32.197



# Known parent->child edges

PC0000 guardproof.info. third.guardproof.info.

 */

Turn that into the following lines by substituting node 
identifiers into the relationships:

# Known domain name nodes

N0000 [label="guardproof.info."] ;

N0002 [label="third.guardproof.info."] ;



# Known address nodes

A0000 [label="61.141.32.197"] ;



# PC0000 guardproof.info. third.guardproof.info.

N0000->N0002 ;



# NA0000 third.guardproof.info. 61.141.32.197

N0002->A0000 ;



/*

# Known name->address edges

NA0000 third.guardproof.info. 61.141.32.197



# Known parent->child edges

PC0000 guardproof.info. third.guardproof.info.

 */

Process that with the 'dot' program, and you have your 
first network diagram.

In addition to the conventional graphic edges, the 
descriptor file includes similar format pair-data that 
describes services, zone records (sub-graphs?), 
blacklisted addresses, and other things which might be 
interesting to include in your graph. This additional 
information could be displayed as different node 
shapes, colors, line sizes, etc.

The descriptor file can also be read and edited by a 
Bash script (of course). You should be able to find 
most of the functions required within the 
"is_spammer.bash" script.

# End Quickstart.



Additional Note
========== ====

Michael Zick points out that there is a "makeviz.bash" interactive
Web site at rediris.es. Can't give the full URL, since this is not
a publically accessible site.

Another anti-spam script.

Example A-31. Spammer Hunt

#!/bin/bash
# whx.sh: "whois" spammer lookup
# Author: Walter Dnes
# Slight revisions (first section) by ABS Guide author.
# Used in ABS Guide with permission.

# Needs version 3.x or greater of Bash to run (because of =~ operator).
# Commented by script author and ABS Guide author.



E_BADARGS=65        # Missing command-line arg.
E_NOHOST=66         # Host not found.
E_TIMEOUT=67        # Host lookup timed out.
E_UNDEF=68          # Some other (undefined) error.
HOSTWAIT=10         # Specify up to 10 seconds for host query reply.
                    # The actual wait may be a bit longer.
OUTFILE=whois.txt   # Output file.
PORT=4321


if [ -z "$1" ]      # Check for (required) command-line arg.
then
  echo "Usage: $0 domain name or IP address"
  exit $E_BADARGS
fi


if [[ "$1" =~ "[a-zA-Z][a-zA-Z]$" ]]  # Ends in two alpha chars?
then                                  # It's a domain name && must do host lookup.
  IPADDR=$(host -W $HOSTWAIT $1 | awk '{print $4}')
                                      # Doing host lookup to get IP address.
				      # Extract final field.
else
  IPADDR="$1"                         # Command-line arg was IP address.
fi

echo; echo "IP Address is: "$IPADDR""; echo

if [ -e "$OUTFILE" ]
then
  rm -f "$OUTFILE"
  echo "Stale output file \"$OUTFILE\" removed."; echo
fi


#  Sanity checks.
#  (This section needs more work.)
#  ===============================
if [ -z "$IPADDR" ]
# No response.
then
  echo "Host not found!"
  exit $E_NOHOST    # Bail out.
fi

if [[ "$IPADDR" =~ "^[;;]" ]]
#  ;; connection timed out; no servers could be reached
then
  echo "Host lookup timed out!"
  exit $E_TIMEOUT   # Bail out.
fi

if [[ "$IPADDR" =~ "[(NXDOMAIN)]$" ]]
#  Host xxxxxxxxx.xxx not found: 3(NXDOMAIN)
then
  echo "Host not found!"
  exit $E_NOHOST    # Bail out.
fi

if [[ "$IPADDR" =~ "[(SERVFAIL)]$" ]]
#  Host xxxxxxxxx.xxx not found: 2(SERVFAIL)
then
  echo "Host not found!"
  exit $E_NOHOST    # Bail out.
fi




# ======================== Main body of script ========================

AFRINICquery() {
#  Define the function that queries AFRINIC. Echo a notification to the
#+ screen, and then run the actual query, redirecting output to $OUTFILE.

  echo "Searching for $IPADDR in whois.afrinic.net"
  whois -h whois.afrinic.net "$IPADDR" > $OUTFILE

#  Check for presence of reference to an rwhois.
#  Warn about non-functional rwhois.infosat.net server
#+ and attempt rwhois query.
  if grep -e "^remarks: .*rwhois\.[^ ]\+" "$OUTFILE"
  then
    echo " " >> $OUTFILE
    echo "***" >> $OUTFILE
    echo "***" >> $OUTFILE
    echo "Warning: rwhois.infosat.net was not working as of 2005/02/02" >> $OUTFILE
    echo "         when this script was written." >> $OUTFILE
    echo "***" >> $OUTFILE
    echo "***" >> $OUTFILE
    echo " " >> $OUTFILE
    RWHOIS=`grep "^remarks: .*rwhois\.[^ ]\+" "$OUTFILE" | tail -n 1 |\
    sed "s/\(^.*\)\(rwhois\..*\)\(:4.*\)/\2/"`
    whois -h ${RWHOIS}:${PORT} "$IPADDR" >> $OUTFILE
  fi
}

APNICquery() {
  echo "Searching for $IPADDR in whois.apnic.net"
  whois -h whois.apnic.net "$IPADDR" > $OUTFILE

#  Just  about  every  country has its own internet registrar.
#  I don't normally bother consulting them, because the regional registry
#+ usually supplies sufficient information.
#  There are a few exceptions, where the regional registry simply
#+ refers to the national registry for direct data.
#  These are Japan and South Korea in APNIC, and Brasil in LACNIC.
#  The following if statement checks $OUTFILE (whois.txt) for the presence
#+ of "KR" (South Korea) or "JP" (Japan) in the country field.
#  If either is found, the query is re-run against the appropriate
#+ national registry.

  if grep -E "^country:[ ]+KR$" "$OUTFILE"
  then
    echo "Searching for $IPADDR in whois.krnic.net"
    whois -h whois.krnic.net "$IPADDR" >> $OUTFILE
  elif grep -E "^country:[ ]+JP$" "$OUTFILE"
  then
    echo "Searching for $IPADDR in whois.nic.ad.jp"
    whois -h whois.nic.ad.jp "$IPADDR"/e >> $OUTFILE
  fi
}

ARINquery() {
  echo "Searching for $IPADDR in whois.arin.net"
  whois -h whois.arin.net "$IPADDR" > $OUTFILE

#  Several large internet providers listed by ARIN have their own
#+ internal whois service, referred to as "rwhois".
#  A large block of IP addresses is listed with the provider
#+ under the ARIN registry.
#  To get the IP addresses of 2nd-level ISPs or other large customers,
#+ one has to refer to the rwhois server on port 4321.
#  I originally started with a bunch of "if" statements checking for
#+ the larger providers.
#  This approach is unwieldy, and there's always another rwhois server
#+ that I didn't know about.
#  A more elegant approach is to check $OUTFILE for a reference
#+ to a whois server, parse that server name out of the comment section,
#+ and re-run the query against the appropriate rwhois server.
#  The parsing looks a bit ugly, with a long continued line inside
#+ backticks.
#  But it only has to be done once, and will work as new servers are added.
#@   ABS Guide author comment: it isn't all that ugly, and is, in fact,
#@+  an instructive use of Regular Expressions.

  if grep -E "^Comment: .*rwhois.[^ ]+" "$OUTFILE"
  then
    RWHOIS=`grep -e "^Comment:.*rwhois\.[^ ]\+" "$OUTFILE" | tail -n 1 |\
    sed "s/^\(.*\)\(rwhois\.[^ ]\+\)\(.*$\)/\2/"`
    echo "Searching for $IPADDR in ${RWHOIS}"
    whois -h ${RWHOIS}:${PORT} "$IPADDR" >> $OUTFILE
  fi
}

LACNICquery() {
  echo "Searching for $IPADDR in whois.lacnic.net"
  whois -h whois.lacnic.net "$IPADDR" > $OUTFILE

#  The  following if statement checks $OUTFILE (whois.txt) for the presence of
#+ "BR" (Brasil) in the country field.
#  If it is found, the query is re-run against whois.registro.br.

  if grep -E "^country:[ ]+BR$" "$OUTFILE"
  then
    echo "Searching for $IPADDR in whois.registro.br"
    whois -h whois.registro.br "$IPADDR" >> $OUTFILE
  fi
}

RIPEquery() {
  echo "Searching for $IPADDR in whois.ripe.net"
  whois -h whois.ripe.net "$IPADDR" > $OUTFILE
}

#  Initialize a few variables.
#  * slash8 is the most significant octet
#  * slash16 consists of the two most significant octets
#  * octet2 is the second most significant octet




slash8=`echo $IPADDR | cut -d. -f 1`
  if [ -z "$slash8" ]  # Yet another sanity check.
  then
    echo "Undefined error!"
    exit $E_UNDEF
  fi
slash16=`echo $IPADDR | cut -d. -f 1-2`
#                             ^ Period specified as 'cut" delimiter.
  if [ -z "$slash16" ]
  then
    echo "Undefined error!"
    exit $E_UNDEF
  fi
octet2=`echo $slash16 | cut -d. -f 2`
  if [ -z "$octet2" ]
  then
    echo "Undefined error!"
    exit $E_UNDEF
  fi


#  Check for various odds and ends of reserved space.
#  There is no point in querying for those addresses.

if [ $slash8 == 0 ]; then
  echo $IPADDR is '"This Network"' space\; Not querying
elif [ $slash8 == 10 ]; then
  echo $IPADDR is RFC1918 space\; Not querying
elif [ $slash8 == 14 ]; then
  echo $IPADDR is '"Public Data Network"' space\; Not querying
elif [ $slash8 == 127 ]; then
  echo $IPADDR is loopback space\; Not querying
elif [ $slash16 == 169.254 ]; then
  echo $IPADDR is link-local space\; Not querying
elif [ $slash8 == 172 ] && [ $octet2 -ge 16 ] && [ $octet2 -le 31 ];then
  echo $IPADDR is RFC1918 space\; Not querying
elif [ $slash16 == 192.168 ]; then
  echo $IPADDR is RFC1918 space\; Not querying
elif [ $slash8 -ge 224 ]; then
  echo $IPADDR is either Multicast or reserved space\; Not querying
elif [ $slash8 -ge 200 ] && [ $slash8 -le 201 ]; then LACNICquery "$IPADDR"
elif [ $slash8 -ge 202 ] && [ $slash8 -le 203 ]; then APNICquery "$IPADDR"
elif [ $slash8 -ge 210 ] && [ $slash8 -le 211 ]; then APNICquery "$IPADDR"
elif [ $slash8 -ge 218 ] && [ $slash8 -le 223 ]; then APNICquery "$IPADDR"

#  If we got this far without making a decision, query ARIN.
#  If a reference is found in $OUTFILE to APNIC, AFRINIC, LACNIC, or RIPE,
#+ query the appropriate whois server.

else
  ARINquery "$IPADDR"
  if grep "whois.afrinic.net" "$OUTFILE"; then
    AFRINICquery "$IPADDR"
  elif grep -E "^OrgID:[ ]+RIPE$" "$OUTFILE"; then
    RIPEquery "$IPADDR"
  elif grep -E "^OrgID:[ ]+APNIC$" "$OUTFILE"; then
    APNICquery "$IPADDR"
  elif grep -E "^OrgID:[ ]+LACNIC$" "$OUTFILE"; then
    LACNICquery "$IPADDR"
  fi
fi

#@  ---------------------------------------------------------------
#   Try also:
#   wget http://logi.cc/nw/whois.php3?ACTION=doQuery&DOMAIN=$IPADDR
#@  ---------------------------------------------------------------

#  We've  now  finished  the querying.
#  Echo a copy of the final result to the screen.

cat $OUTFILE
# Or "less $OUTFILE" . . .


exit 0

#@  ABS Guide author comments:
#@  Nothing fancy here, but still a very useful tool for hunting spammers.
#@  Sure, the script can be cleaned up some, and it's still a bit buggy,
#@+ (exercise for reader), but all the same, it's a nice piece of coding
#@+ by Walter Dnes.
#@  Thank you!

"Little Monster's" front end to wget.

Example A-32. Making wget easier to use

#!/bin/bash
# wgetter2.bash

# Author: Little Monster [monster@monstruum.co.uk]
# ==> Used in ABS Guide with permission of script author.
# ==> This script still needs debugging and fixups (exercise for reader).
# ==> It could also use some additional editing in the comments.


#  This is wgetter2 --
#+ a Bash script to make wget a bit more friendly, and save typing.

#  Carefully crafted by Little Monster.
#  More or less complete on 02/02/2005.
#  If you think this script can be improved,
#+ email me at: monster@monstruum.co.uk
# ==> and cc: to the author of the ABS Guide, please.
#  This script is licenced under the GPL.
#  You are free to copy, alter and re-use it,
#+ but please don't try to claim you wrote it.
#  Log your changes here instead.

# =======================================================================
# changelog:

# 07/02/2005.  Fixups by Little Monster.
# 02/02/2005.  Minor additions by Little Monster.
#              (See after # +++++++++++ )
# 29/01/2005.  Minor stylistic edits and cleanups by author of ABS Guide.
#              Added exit error codes.
# 22/11/2004.  Finished initial version of second version of wgetter:
#              wgetter2 is born.
# 01/12/2004.  Changed 'runn' function so it can be run 2 ways --
#              either ask for a file name or have one input on the CL.
# 01/12/2004.  Made sensible handling of no URL's given.
# 01/12/2004.  Made loop of main options, so you don't
#              have to keep calling wgetter 2 all the time.
#              Runs as a session instead.
# 01/12/2004.  Added looping to 'runn' function.
#              Simplified and improved.
# 01/12/2004.  Added state to recursion setting.
#              Enables re-use of previous value.
# 05/12/2004.  Modified the file detection routine in the 'runn' function
#              so it's not fooled by empty values, and is cleaner.
# 01/02/2004.  Added cookie finding routine from later version (which 
#              isn't ready yet), so as not to have hard-coded paths.
# =======================================================================

# Error codes for abnormal exit.
E_USAGE=67        # Usage message, then quit.
E_NO_OPTS=68      # No command-line args entered.
E_NO_URLS=69      # No URLs passed to script.
E_NO_SAVEFILE=70  # No save filename passed to script.
E_USER_EXIT=71    # User decides to quit.


#  Basic default wget command we want to use.
#  This is the place to change it, if required.
#  NB: if using a proxy, set http_proxy = yourproxy in .wgetrc.
#  Otherwise delete --proxy=on, below.
# ====================================================================
CommandA="wget -nc -c -t 5 --progress=bar --random-wait --proxy=on -r"
# ====================================================================



# --------------------------------------------------------------------
# Set some other variables and explain them.

pattern=" -A .jpg,.JPG,.jpeg,.JPEG,.gif,.GIF,.htm,.html,.shtml,.php"
                    # wget's option to only get certain types of file.
                    # comment out if not using
today=`date +%F`    # Used for a filename.
home=$HOME          # Set HOME to an internal variable.
                    # In case some other path is used, change it here.
depthDefault=3      # Set a sensible default recursion.
Depth=$depthDefault # Otherwise user feedback doesn't tie in properly.
RefA=""             # Set blank referring page.
Flag=""             #  Default to not saving anything,
                    #+ or whatever else might be wanted in future.
lister=""           # Used for passing a list of urls directly to wget.
Woptions=""         # Used for passing wget some options for itself.
inFile=""           # Used for the run function.
newFile=""          # Used for the run function.
savePath="$home/w-save"
Config="$home/.wgetter2rc"
                    #  This is where some variables can be stored, 
                    #+ if permanently changed from within the script.
Cookie_List="$home/.cookielist"
                    # So we know where the cookies are kept . . .
cFlag=""            # Part of the cookie file selection routine.

# Define the options available. Easy to change letters here if needed.
# These are the optional options; you don't just wait to be asked.

save=s   # Save command instead of executing it.
cook=c   # Change cookie file for this session.
help=h   # Usage guide.
list=l   # Pass wget the -i option and URL list.
runn=r   # Run saved commands as an argument to the option.
inpu=i   # Run saved commands interactively.
wopt=w   # Allow to enter options to pass directly to wget.
# --------------------------------------------------------------------


if [ -z "$1" ]; then   # Make sure we get something for wget to eat.
   echo "You must at least enter a URL or option!"
   echo "-$help for usage."
   exit $E_NO_OPTS
fi



# +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
# added added added added added added added added added added added added

if [ ! -e "$Config" ]; then   # See if configuration file exists.
   echo "Creating configuration file, $Config"
   echo "# This is the configuration file for wgetter2" > "$Config"
   echo "# Your customised settings will be saved in this file" >> "$Config"
else
   source $Config             # Import variables we set outside the script.
fi

if [ ! -e "$Cookie_List" ]; then
   # Set up a list of cookie files, if there isn't one.
   echo "Hunting for cookies . . ."
   find -name cookies.txt >> $Cookie_List # Create the list of cookie files.
fi #  Isolate this in its own 'if' statement,
   #+ in case we got interrupted while searching.

if [ -z "$cFlag" ]; then # If we haven't already done this . . .
   echo                  # Make a nice space after the command prompt.
   echo "Looks like you haven't set up your source of cookies yet."
   n=0                   #  Make sure the counter
                         #+ doesn't contain random values.
   while read; do
      Cookies[$n]=$REPLY # Put the cookie files we found into an array.
      echo "$n) ${Cookies[$n]}"  # Create a menu.
      n=$(( n + 1 ))     # Increment the counter.
   done < $Cookie_List   # Feed the read statement.
   echo "Enter the number of the cookie file you want to use."
   echo "If you won't be using cookies, just press RETURN."
   echo
   echo "I won't be asking this again. Edit $Config"
   echo "If you decide to change at a later date"
   echo "or use the -${cook} option for per session changes."
   read
   if [ ! -z $REPLY ]; then   # User didn't just press return.
      Cookie=" --load-cookies ${Cookies[$REPLY]}"
      # Set the variable here as well as in the config file.

      echo "Cookie=\" --load-cookies ${Cookies[$REPLY]}\"" >> $Config
   fi
   echo "cFlag=1" >> $Config  # So we know not to ask again.
fi

# end added section end added section end added section end added section
# +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++



# Another variable.
# This one may or may not be subject to variation.
# A bit like the small print.
CookiesON=$Cookie
# echo "cookie file is $CookiesON" # For debugging.
# echo "home is ${home}"           # For debugging.
                                   # Got caught with this one!


wopts()
{
echo "Enter options to pass to wget."
echo "It is assumed you know what you're doing."
echo
echo "You can pass their arguments here too."
# That is to say, everything passed here is passed to wget.

read Wopts
# Read in the options to be passed to wget.

Woptions=" $Wopts"
#         ^  Why the leading space?
# Assign to another variable.
# Just for fun, or something . . .

echo "passing options ${Wopts} to wget"
# Mainly for debugging.
# Is cute.

return
}


save_func()
{
echo "Settings will be saved."
if [ ! -d $savePath ]; then  #  See if directory exists.
   mkdir $savePath           #  Create the directory to save things in
                             #+ if it isn't already there.
fi

Flag=S
# Tell the final bit of code what to do.
# Set a flag since stuff is done in main.

return
}


usage() # Tell them how it works.
{
    echo "Welcome to wgetter.  This is a front end to wget."
    echo "It will always run wget with these options:"
    echo "$CommandA"
    echo "and the pattern to match: $pattern \
(which you can change at the top of this script)."
    echo "It will also ask you for recursion depth, \
and if you want to use a referring page."
    echo "Wgetter accepts the following options:"
    echo ""
    echo "-$help : Display this help."
    echo "-$save : Save the command to a file $savePath/wget-($today) \
instead of running it."
    echo "-$runn : Run saved wget commands instead of starting a new one -"
    echo "Enter filename as argument to this option."
    echo "-$inpu : Run saved wget commands interactively --"
    echo "The script will ask you for the filename."
    echo "-$cook : Change the cookies file for this session."
    echo "-$list : Tell wget to use URL's from a list instead of \
from the command-line."
    echo "-$wopt : Pass any other options direct to wget."
    echo ""
    echo "See the wget man page for additional options \
you can pass to wget."
    echo ""

    exit $E_USAGE  # End here. Don't process anything else.
}



list_func() #  Gives the user the option to use the -i option to wget,
            #+ and a list of URLs.
{
while [ 1 ]; do
   echo "Enter the name of the file containing URL's (press q to change
your mind)."
   read urlfile
   if [ ! -e "$urlfile" ] && [ "$urlfile" != q ]; then
       # Look for a file, or the quit option.
       echo "That file does not exist!"
   elif [ "$urlfile" = q ]; then # Check quit option.
       echo "Not using a url list."
       return
   else
      echo "using $urlfile."
      echo "If you gave url's on the command-line, I'll use those first."
                            # Report wget standard behaviour to the user.
      lister=" -i $urlfile" # This is what we want to pass to wget.
      return
   fi
done
}


cookie_func() # Give the user the option to use a different cookie file.
{
while [ 1 ]; do
   echo "Change the cookies file. Press return if you don't want to change 
it."
   read Cookies
   # NB: this is not the same as Cookie, earlier.
   # There is an 's' on the end.
   # Bit like chocolate chips.
   if [ -z "$Cookies" ]; then                 # Escape clause for wusses.
      return
   elif [ ! -e "$Cookies" ]; then
      echo "File does not exist.  Try again." # Keep em going . . .
   else
       CookiesON=" --load-cookies $Cookies"   # File is good -- use it!
       return
   fi
done
}



run_func()
{
if [ -z "$OPTARG" ]; then
# Test to see if we used the in-line option or the query one.
   if [ ! -d "$savePath" ]; then      # If directory doesn't exist . . .
      echo "$savePath does not appear to exist."
      echo "Please supply path and filename of saved wget commands:"
      read newFile
         until [ -f "$newFile" ]; do  # Keep going till we get something.
            echo "Sorry, that file does not exist.  Please try again."
            # Try really hard to get something.
            read newFile
         done


# -----------------------------------------------------------------------
#       if [ -z ( grep wget ${newfile} ) ]; then
        # Assume they haven't got the right file and bail out.
#       echo "Sorry, that file does not contain wget commands.  Aborting."
#       exit
#       fi
#
# This is bogus code.
# It doesn't actually work.
# If anyone wants to fix it, feel free!
# -----------------------------------------------------------------------


      filePath="${newFile}"
   else
   echo "Save path is $savePath"
     echo "Please enter name of the file which you want to use."
     echo "You have a choice of:"
     ls $savePath                                    # Give them a choice.
     read inFile
       until [ -f "$savePath/$inFile" ]; do         #  Keep going till
                                                    #+ we get something.
          if [ ! -f "${savePath}/${inFile}" ]; then # If file doesn't exist.
             echo "Sorry, that file does not exist.  Please choose from:"
             ls $savePath                           # If a mistake is made.
             read inFile
          fi
         done
      filePath="${savePath}/${inFile}"  # Make one variable . . .
   fi
else filePath="${savePath}/${OPTARG}"   # Which can be many things . . .
fi

if [ ! -f "$filePath" ]; then           # If a bogus file got through.
   echo "You did not specify a suitable file."
   echo "Run this script with the -${save} option first."
   echo "Aborting."
   exit $E_NO_SAVEFILE
fi
echo "Using: $filePath"
while read; do
    eval $REPLY
    echo "Completed: $REPLY"
done < $filePath  # Feed the actual file we are using into a 'while' loop.

exit
}



# Fish out any options we are using for the script.
# This is based on the demo in "Learning The Bash Shell" (O'Reilly).
while getopts ":$save$cook$help$list$runn:$inpu$wopt" opt
do
  case $opt in
     $save) save_func;;   #  Save some wgetter sessions for later.
     $cook) cookie_func;; #  Change cookie file.
     $help) usage;;       #  Get help.
     $list) list_func;;   #  Allow wget to use a list of URLs.
     $runn) run_func;;    #  Useful if you are calling wgetter from,
                          #+ for example, a cron script.
     $inpu) run_func;;    #  When you don't know what your files are named.
     $wopt) wopts;;       #  Pass options directly to wget.
        \?) echo "Not a valid option."
            echo "Use -${wopt} to pass options directly to wget,"
            echo "or -${help} for help";;      # Catch anything else.
  esac
done
shift $((OPTIND - 1))     # Do funky magic stuff with $#.


if [ -z "$1" ] && [ -z "$lister" ]; then
                          #  We should be left with at least one URL
                          #+ on the command-line, unless a list is 
			  #+ being used -- catch empty CL's.
   echo "No URL's given! You must enter them on the same line as wgetter2."
   echo "E.g.,  wgetter2 http://somesite http://anothersite."
   echo "Use $help option for more information."
   exit $E_NO_URLS        # Bail out, with appropriate error code.
fi

URLS=" $@"
# Use this so that URL list can be changed if we stay in the option loop.

while [ 1 ]; do
   # This is where we ask for the most used options.
   # (Mostly unchanged from version 1 of wgetter)
   if [ -z $curDepth ]; then
      Current=""
   else Current=" Current value is $curDepth"
   fi
       echo "How deep should I go? \
(integer: Default is $depthDefault.$Current)"
       read Depth   # Recursion -- how far should we go?
       inputB=""    # Reset this to blank on each pass of the loop.
       echo "Enter the name of the referring page (default is none)."
       read inputB  # Need this for some sites.

       echo "Do you want to have the output logged to the terminal"
       echo "(y/n, default is yes)?"
       read noHide  # Otherwise wget will just log it to a file.

       case $noHide in    # Now you see me, now you don't.
          y|Y ) hide="";;
          n|N ) hide=" -b";;
            * ) hide="";;
       esac

       if [ -z ${Depth} ]; then
       #  User accepted either default or current depth,
       #+ in which case Depth is now empty.
          if [ -z ${curDepth} ]; then
          #  See if a depth was set on a previous iteration.
             Depth="$depthDefault"
             #  Set the default recursion depth if nothing
             #+ else to use.
          else Depth="$curDepth" #  Otherwise, set the one we used before.
          fi
       fi
   Recurse=" -l $Depth"          # Set how deep we want to go.
   curDepth=$Depth               # Remember setting for next time.

       if [ ! -z $inputB ]; then
          RefA=" --referer=$inputB"   # Option to use referring page.
       fi

   WGETTER="${CommandA}${pattern}${hide}${RefA}${Recurse}\
${CookiesON}${lister}${Woptions}${URLS}"
   #  Just string the whole lot together . . .
   #  NB: no embedded spaces.
   #  They are in the individual elements so that if any are empty,
   #+ we don't get an extra space.

   if [ -z "${CookiesON}" ] && [ "$cFlag" = "1" ] ; then
       echo "Warning -- can't find cookie file"
       #  This should be changed,
       #+ in case the user has opted to not use cookies.
   fi

   if [ "$Flag" = "S" ]; then
      echo "$WGETTER" >> $savePath/wget-${today}
      #  Create a unique filename for today, or append to it if it exists.
      echo "$inputB" >> $savePath/site-list-${today}
      #  Make a list, so it's easy to refer back to,
      #+ since the whole command is a bit confusing to look at.
      echo "Command saved to the file $savePath/wget-${today}"
           # Tell the user.
      echo "Referring page URL saved to the file$ \
savePath/site-list-${today}"
           # Tell the user.
      Saver=" with save option"
      # Stick this somewhere, so it appears in the loop if set.
   else
       echo "*****************"
       echo "*****Getting*****"
       echo "*****************"
       echo ""
       echo "$WGETTER"
       echo ""
       echo "*****************"
       eval "$WGETTER"
   fi

       echo ""
       echo "Starting over$Saver."
       echo "If you want to stop, press q."
       echo "Otherwise, enter some URL's:"
       # Let them go again. Tell about save option being set.

       read
       case $REPLY in
       # Need to change this to a 'trap' clause.
          q|Q ) exit $E_USER_EXIT;;  # Exercise for the reader?
            * ) URLS=" $REPLY";;
       esac

       echo ""
done


exit 0

Example A-33. A podcasting script

#!/bin/bash

#  bashpodder.sh:
#  By Linc 10/1/2004
#  Find the latest script at
#+ http://linc.homeunix.org:8080/scripts/bashpodder
#  Last revision 12/14/2004 - Many Contributors!
#  If you use this and have made improvements or have comments
#+ drop me an email at linc dot fessenden at gmail dot com
#  I'd appreciate it!

# ==>  ABS Guide extra comments.

# ==>  Author of this script has kindly granted permission
# ==>+ for inclusion in ABS Guide.


# ==> ################################################################
# 
# ==> What is "podcasting"?

# ==> It's broadcasting "radio shows" over the Internet.
# ==> These shows can be played on iPods and other music file players.

# ==> This script makes it possible.
# ==> See documentation at the script author's site, above.

# ==> ################################################################


# Make script crontab friendly:
cd $(dirname $0)
# ==> Change to directory where this script lives.

# datadir is the directory you want podcasts saved to:
datadir=$(date +%Y-%m-%d)
# ==> Will create a date-labeled directory, named: YYYY-MM-DD

# Check for and create datadir if necessary:
if test ! -d $datadir
        then
        mkdir $datadir
fi

# Delete any temp file:
rm -f temp.log

#  Read the bp.conf file and wget any url not already
#+ in the podcast.log file:
while read podcast
  do # ==> Main action follows.
  file=$(wget -q $podcast -O - | tr '\r' '\n' | tr \' \" | \
sed -n 's/.*url="\([^"]*\)".*/\1/p')
  for url in $file
                do
                echo $url >> temp.log
                if ! grep "$url" podcast.log > /dev/null
                        then
                        wget -q -P $datadir "$url"
                fi
                done
    done < bp.conf

# Move dynamically created log file to permanent log file:
cat podcast.log >> temp.log
sort temp.log | uniq > podcast.log
rm temp.log
# Create an m3u playlist:
ls $datadir | grep -v m3u > $datadir/podcast.m3u


exit 0

#################################################
For a different scripting approach to Podcasting,
see Phil Salkie's article, 
"Internet Radio to Podcast with Shell Tools"
in the September, 2005 issue of LINUX JOURNAL,
http://www.linuxjournal.com/article/8171
#################################################

Example A-34. Nightly backup to a firewire HD

#!/bin/bash
# nightly-backup.sh
# http://www.richardneill.org/source.php#nightly-backup-rsync
# Copyright (c) 2005 Richard Neill <backup@richardneill.org>.
# This is Free Software licensed under the GNU GPL.
# ==> Included in ABS Guide with script author's kind permission.
# ==> (Thanks!)

#  This does a backup from the host computer to a locally connected
#+ firewire HDD using rsync and ssh.
#  It then rotates the backups.
#  Run it via cron every night at 5am.
#  This only backs up the home directory.
#  If ownerships (other than the user's) should be preserved,
#+ then run the rsync process as root (and re-instate the -o).
#  We save every day for 7 days, then every week for 4 weeks,
#+ then every month for 3 months.

#  See: http://www.mikerubel.org/computers/rsync_snapshots/
#+ for more explanation of the theory.
#  Save as: $HOME/bin/nightly-backup_firewire-hdd.sh

#  Known bugs:
#  ----------
#  i)  Ideally, we want to exclude ~/.tmp and the browser caches.

#  ii) If the user is sitting at the computer at 5am,
#+     and files are modified while the rsync is occurring,
#+     then the BACKUP_JUSTINCASE branch gets triggered.
#      To some extent, this is a 
#+     feature, but it also causes a "disk-space leak".





##### BEGIN CONFIGURATION SECTION ############################################
LOCAL_USER=rjn                # User whose home directory should be backed up.
MOUNT_POINT=/backup           # Mountpoint of backup drive.
                              # NO trailing slash!
                              # This must be unique (eg using a udev symlink)
SOURCE_DIR=/home/$LOCAL_USER  # NO trailing slash - it DOES matter to rsync.
BACKUP_DEST_DIR=$MOUNT_POINT/backup/`hostname -s`.${LOCAL_USER}.nightly_backup
DRY_RUN=false                 #If true, invoke rsync with -n, to do a dry run.
                              # Comment out or set to false for normal use.
VERBOSE=false                 # If true, make rsync verbose.
                              # Comment out or set to false otherwise.
COMPRESS=false                # If true, compress.
                              # Good for internet, bad on LAN.
                              # Comment out or set to false otherwise.

### Exit Codes ###
E_VARS_NOT_SET=64
E_COMMANDLINE=65
E_MOUNT_FAIL=70
E_NOSOURCEDIR=71
E_UNMOUNTED=72
E_BACKUP=73
##### END CONFIGURATION SECTION ##############################################


# Check that all the important variables have been set:
if [ -z "$LOCAL_USER" ] ||
   [ -z "$SOURCE_DIR" ] ||
   [ -z "$MOUNT_POINT" ]  ||
   [ -z "$BACKUP_DEST_DIR" ]
then
   echo 'One of the variables is not set! Edit the file: $0. BACKUP FAILED.'
   exit $E_VARS_NOT_SET
fi

if [ "$#" != 0 ]  # If command-line param(s) . . .
then              # Here document(ation).
  cat <<-ENDOFTEXT
    Automatic Nightly backup run from cron.
    Read the source for more details: $0
    The backup directory is $BACKUP_DEST_DIR .
    It will be created if necessary; initialisation is no longer required.

    WARNING: Contents of $BACKUP_DEST_DIR are rotated.
    Directories named 'backup.\$i' will eventually be DELETED.
    We keep backups from every day for 7 days (1-8),
    then every week for 4 weeks (9-12),
    then every month for 3 months (13-15).

    You may wish to add this to your crontab using 'crontab -e'
    #  Back up files: $SOURCE_DIR to $BACKUP_DEST_DIR
    #+ every night at 3:15 am
         15 03 * * * /home/$LOCAL_USER/bin/nightly-backup_firewire-hdd.sh

    Don't forget to verify the backups are working,
    especially if you don't read cron's mail!"
	ENDOFTEXT
   exit $E_COMMANDLINE
fi


# Parse the options.
# ==================

if [ "$DRY_RUN" == "true" ]; then
  DRY_RUN="-n"
  echo "WARNING:"
  echo "THIS IS A 'DRY RUN'!"
  echo "No data will actually be transferred!"
else
  DRY_RUN=""
fi

if [ "$VERBOSE" == "true" ]; then
  VERBOSE="-v"
else
  VERBOSE=""
fi

if [ "$COMPRESS" == "true" ]; then
  COMPRESS="-z"
else
  COMPRESS=""
fi


#  Every week (actually of 8 days) and every month,
#+ extra backups are preserved.
DAY_OF_MONTH=`date +%d`            # Day of month (01..31).
if [ $DAY_OF_MONTH = 01 ]; then    # First of month.
  MONTHSTART=true
elif [ $DAY_OF_MONTH = 08 \
    -o $DAY_OF_MONTH = 16 \
    -o $DAY_OF_MONTH = 24 ]; then
    # Day 8,16,24  (use 8, not 7 to better handle 31-day months)
      WEEKSTART=true
fi



#  Check that the HDD is mounted.
#  At least, check that *something* is mounted here!
#  We can use something unique to the device, rather than just guessing
#+ the scsi-id by having an appropriate udev rule in
#+ /etc/udev/rules.d/10-rules.local
#+ and by putting a relevant entry in /etc/fstab.
#  Eg: this udev rule:
# BUS="scsi", KERNEL="sd*", SYSFS{vendor}="WDC WD16",
# SYSFS{model}="00JB-00GVA0     ", NAME="%k", SYMLINK="lacie_1394d%n"

if mount | grep $MOUNT_POINT >/dev/null; then
  echo "Mount point $MOUNT_POINT is indeed mounted. OK"
else
  echo -n "Attempting to mount $MOUNT_POINT..."	
           # If it isn't mounted, try to mount it.
  sudo mount $MOUNT_POINT 2>/dev/null

  if mount | grep $MOUNT_POINT >/dev/null; then
    UNMOUNT_LATER=TRUE
    echo "OK"
    #  Note: Ensure that this is also unmounted
    #+ if we exit prematurely with failure.
  else
    echo "FAILED"
    echo -e "Nothing is mounted at $MOUNT_POINT. BACKUP FAILED!"
    exit $E_MOUNT_FAIL
  fi
fi


# Check that source dir exists and is readable.
if [ ! -r  $SOURCE_DIR ] ; then
  echo "$SOURCE_DIR does not exist, or cannot be read. BACKUP FAILED."
  exit $E_NOSOURCEDIR
fi


# Check that the backup directory structure is as it should be.
# If not, create it.
# Create the subdirectories.
# Note that backup.0 will be created as needed by rsync.

for ((i=1;i<=15;i++)); do
  if [ ! -d $BACKUP_DEST_DIR/backup.$i ]; then
    if /bin/mkdir -p $BACKUP_DEST_DIR/backup.$i ; then
    #  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^  No [ ] test brackets. Why?
      echo "Warning: directory $BACKUP_DEST_DIR/backup.$i is missing,"
      echo "or was not initialised. (Re-)creating it."
    else
      echo "ERROR: directory $BACKUP_DEST_DIR/backup.$i"
      echo "is missing and could not be created."
    if  [ "$UNMOUNT_LATER" == "TRUE" ]; then
        # Before we exit, unmount the mount point if necessary.
        cd
	sudo umount $MOUNT_POINT &&
	echo "Unmounted $MOUNT_POINT again. Giving up."
    fi
      exit $E_UNMOUNTED
  fi
fi
done


#  Set the permission to 700 for security
#+ on an otherwise permissive multi-user system.
if ! /bin/chmod 700 $BACKUP_DEST_DIR ; then
  echo "ERROR: Could not set permissions on $BACKUP_DEST_DIR to 700."

  if  [ "$UNMOUNT_LATER" == "TRUE" ]; then
  # Before we exit, unmount the mount point if necessary.
     cd ; sudo umount $MOUNT_POINT \
     && echo "Unmounted $MOUNT_POINT again. Giving up."
  fi

  exit $E_UNMOUNTED
fi

# Create the symlink: current -> backup.1 if required.
# A failure here is not critical.
cd $BACKUP_DEST_DIR
if [ ! -h current ] ; then
  if ! /bin/ln -s backup.1 current ; then
    echo "WARNING: could not create symlink current -> backup.1"
  fi
fi


# Now, do the rsync.
echo "Now doing backup with rsync..."
echo "Source dir: $SOURCE_DIR"
echo -e "Backup destination dir: $BACKUP_DEST_DIR\n"


/usr/bin/rsync $DRY_RUN $VERBOSE -a -S --delete --modify-window=60 \
--link-dest=../backup.1 $SOURCE_DIR $BACKUP_DEST_DIR/backup.0/

#  Only warn, rather than exit if the rsync failed,
#+ since it may only be a minor problem.
#  E.g., if one file is not readable, rsync will fail.
#  This shouldn't prevent the rotation.
#  Not using, e.g., `date +%a`  since these directories
#+ are just full of links and don't consume *that much* space.

if [ $? != 0 ]; then
  BACKUP_JUSTINCASE=backup.`date +%F_%T`.justincase
  echo "WARNING: the rsync process did not entirely succeed."
  echo "Something might be wrong."
  echo "Saving an extra copy at: $BACKUP_JUSTINCASE"
  echo "WARNING: if this occurs regularly, a LOT of space will be consumed,"
  echo "even though these are just hard-links!"
fi

# Save a readme in the backup parent directory.
# Save another one in the recent subdirectory.
echo "Backup of $SOURCE_DIR on `hostname` was last run on \
`date`" > $BACKUP_DEST_DIR/README.txt
echo "This backup of $SOURCE_DIR on `hostname` was created on \
`date`" > $BACKUP_DEST_DIR/backup.0/README.txt

# If we are not in a dry run, rotate the backups.
[ -z "$DRY_RUN" ] &&

  #  Check how full the backup disk is.
  #  Warn if 90%. if 98% or more, we'll probably fail, so give up.
  #  (Note: df can output to more than one line.)
  #  We test this here, rather than before
  #+ so that rsync may possibly have a chance.
  DISK_FULL_PERCENT=`/bin/df $BACKUP_DEST_DIR |
  tr "\n" ' ' | awk '{print $12}' | grep -oE [0-9]+ `
  echo "Disk space check on backup partition \
  $MOUNT_POINT $DISK_FULL_PERCENT% full."
  if [ $DISK_FULL_PERCENT -gt 90 ]; then
    echo "Warning: Disk is greater than 90% full."
  fi
  if [ $DISK_FULL_PERCENT -gt 98 ]; then
    echo "Error: Disk is full! Giving up."
      if  [ "$UNMOUNT_LATER" == "TRUE" ]; then
        # Before we exit, unmount the mount point if necessary.
        cd; sudo umount $MOUNT_POINT &&
        echo "Unmounted $MOUNT_POINT again. Giving up."
      fi
    exit $E_UNMOUNTED
  fi


 # Create an extra backup.
 # If this copy fails, give up.
 if [ -n "$BACKUP_JUSTINCASE" ]; then
   if ! /bin/cp -al $BACKUP_DEST_DIR/backup.0 \
      $BACKUP_DEST_DIR/$BACKUP_JUSTINCASE
   then
     echo "ERROR: Failed to create extra copy \
     $BACKUP_DEST_DIR/$BACKUP_JUSTINCASE"
     if  [ "$UNMOUNT_LATER" == "TRUE" ]; then
       # Before we exit, unmount the mount point if necessary.
       cd ;sudo umount $MOUNT_POINT &&
       echo "Unmounted $MOUNT_POINT again. Giving up."
     fi
     exit $E_UNMOUNTED
   fi
 fi


 # At start of month, rotate the oldest 8.
 if [ "$MONTHSTART" == "true" ]; then
   echo -e "\nStart of month. \
   Removing oldest backup: $BACKUP_DEST_DIR/backup.15"  &&
   /bin/rm -rf  $BACKUP_DEST_DIR/backup.15  &&
   echo "Rotating monthly,weekly backups: \
   $BACKUP_DEST_DIR/backup.[8-14] -> $BACKUP_DEST_DIR/backup.[9-15]"  &&
     /bin/mv $BACKUP_DEST_DIR/backup.14 $BACKUP_DEST_DIR/backup.15  &&
     /bin/mv $BACKUP_DEST_DIR/backup.13 $BACKUP_DEST_DIR/backup.14  &&
     /bin/mv $BACKUP_DEST_DIR/backup.12 $BACKUP_DEST_DIR/backup.13  &&
     /bin/mv $BACKUP_DEST_DIR/backup.11 $BACKUP_DEST_DIR/backup.12  &&
     /bin/mv $BACKUP_DEST_DIR/backup.10 $BACKUP_DEST_DIR/backup.11  &&
     /bin/mv $BACKUP_DEST_DIR/backup.9 $BACKUP_DEST_DIR/backup.10  &&
     /bin/mv $BACKUP_DEST_DIR/backup.8 $BACKUP_DEST_DIR/backup.9

 # At start of week, rotate the second-oldest 4.
 elif [ "$WEEKSTART" == "true" ]; then
   echo -e "\nStart of week. \
   Removing oldest weekly backup: $BACKUP_DEST_DIR/backup.12"  &&
   /bin/rm -rf  $BACKUP_DEST_DIR/backup.12  &&

   echo "Rotating weekly backups: \
   $BACKUP_DEST_DIR/backup.[8-11] -> $BACKUP_DEST_DIR/backup.[9-12]"  &&
     /bin/mv $BACKUP_DEST_DIR/backup.11 $BACKUP_DEST_DIR/backup.12  &&
     /bin/mv $BACKUP_DEST_DIR/backup.10 $BACKUP_DEST_DIR/backup.11  &&
     /bin/mv $BACKUP_DEST_DIR/backup.9 $BACKUP_DEST_DIR/backup.10  &&
     /bin/mv $BACKUP_DEST_DIR/backup.8 $BACKUP_DEST_DIR/backup.9

 else
   echo -e "\nRemoving oldest daily backup: $BACKUP_DEST_DIR/backup.8"  &&
     /bin/rm -rf  $BACKUP_DEST_DIR/backup.8

 fi  &&

 # Every day, rotate the newest 8.
 echo "Rotating daily backups: \
 $BACKUP_DEST_DIR/backup.[1-7] -> $BACKUP_DEST_DIR/backup.[2-8]"  &&
     /bin/mv $BACKUP_DEST_DIR/backup.7 $BACKUP_DEST_DIR/backup.8  &&
     /bin/mv $BACKUP_DEST_DIR/backup.6 $BACKUP_DEST_DIR/backup.7  &&
     /bin/mv $BACKUP_DEST_DIR/backup.5 $BACKUP_DEST_DIR/backup.6  &&
     /bin/mv $BACKUP_DEST_DIR/backup.4 $BACKUP_DEST_DIR/backup.5  &&
     /bin/mv $BACKUP_DEST_DIR/backup.3 $BACKUP_DEST_DIR/backup.4  &&
     /bin/mv $BACKUP_DEST_DIR/backup.2 $BACKUP_DEST_DIR/backup.3  &&
     /bin/mv $BACKUP_DEST_DIR/backup.1 $BACKUP_DEST_DIR/backup.2  &&
     /bin/mv $BACKUP_DEST_DIR/backup.0 $BACKUP_DEST_DIR/backup.1  &&

 SUCCESS=true


if  [ "$UNMOUNT_LATER" == "TRUE" ]; then
  # Unmount the mount point if it wasn't mounted to begin with.
  cd ; sudo umount $MOUNT_POINT && echo "Unmounted $MOUNT_POINT again."
fi


if [ "$SUCCESS" == "true" ]; then
  echo 'SUCCESS!'
  exit 0
fi

# Should have already exited if backup worked.
echo 'BACKUP FAILED! Is this just a dry run? Is the disk full?) '
exit $E_BACKUP

Example A-35. An expanded cd command

###########################################################################
#
#       cdll
#       by Phil Braham
#
#       ############################################
#       Latest version of this script available from
#       http://freshmeat.net/projects/cd/
#       ############################################
#
#       .cd_new
#
#       An enhancement of the Unix cd command
#
#       There are unlimited stack entries and special entries. The stack
#       entries keep the last cd_maxhistory
#       directories that have been used. The special entries can be
#       assigned to commonly used directories.
#
#       The special entries may be pre-assigned by setting the environment
#       variables CDSn or by using the -u or -U command.
#
#       The following is a suggestion for the .profile file:
#
#               . cdll              #  Set up the cd command
#       alias cd='cd_new'           #  Replace the cd command
#               cd -U               #  Upload pre-assigned entries for
#                                   #+ the stack and special entries
#               cd -D               #  Set non-default mode
#               alias @="cd_new @"  #  Allow @ to be used to get history
#
#       For help type:
#
#               cd -h or
#               cd -H
#
#
###########################################################################
#
#       Version 1.2.1
#
#       Written by Phil Braham - Realtime Software Pty Ltd
#       (realtime@mpx.com.au)
#       Please send any suggestions or enhancements to the author (also at
#       phil@braham.net)
#
############################################################################

cd_hm ()
{
        ${PRINTF} "%s" "cd [dir] [0-9] [@[s|h] [-g [<dir>]] [-d] \
[-D] [-r<n>] [dir|0-9] [-R<n>] [<dir>|0-9]
   [-s<n>] [-S<n>] [-u] [-U] [-f] [-F] [-h] [-H] [-v]
    <dir> Go to directory
    0-n         Go to previous directory (0 is previous, 1 is last but 1 etc)
                n is up to max history (default is 50)
    @           List history and special entries
    @h          List history entries
    @s          List special entries
    -g [<dir>]  Go to literal name (bypass special names)
                This is to allow access to dirs called '0','1','-h' etc
    -d          Change default action - verbose. (See note)
    -D          Change default action - silent. (See note)
    -s<n> Go to the special entry <n>*
    -S<n> Go to the special entry <n>
                and replace it with the current dir*
    -r<n> [<dir>] Go to directory <dir>
                              and then put it on special entry <n>*
    -R<n> [<dir>] Go to directory <dir>
                              and put current dir on special entry <n>*
    -a<n>       Alternative suggested directory. See note below.
    -f [<file>] File entries to <file>.
    -u [<file>] Update entries from <file>.
                If no filename supplied then default file
                (${CDPath}${2:-"$CDFile"}) is used
                -F and -U are silent versions
    -v          Print version number
    -h          Help
    -H          Detailed help

    *The special entries (0 - 9) are held until log off, replaced by another
     entry or updated with the -u command

    Alternative suggested directories:
    If a directory is not found then CD will suggest any
    possibilities. These are directories starting with the same letters
    and if any are found they are listed prefixed with -a<n>
    where <n> is a number.
    It's possible to go to the directory by entering cd -a<n>
    on the command line.
    
    The directory for -r<n> or -R<n> may be a number.
    For example:
        $ cd -r3 4  Go to history entry 4 and put it on special entry 3
        $ cd -R3 4  Put current dir on the special entry 3
                    and go to history entry 4
        $ cd -s3    Go to special entry 3
    
    Note that commands R,r,S and s may be used without a number
    and refer to 0:
        $ cd -s     Go to special entry 0
        $ cd -S     Go to special entry 0 and make special
                    entry 0 current dir
        $ cd -r 1   Go to history entry 1 and put it on special entry 0
        $ cd -r     Go to history entry 0 and put it on special entry 0
    "
        if ${TEST} "$CD_MODE" = "PREV"
        then
                ${PRINTF} "$cd_mnset"
        else
                ${PRINTF} "$cd_mset"
        fi
}

cd_Hm ()
{
        cd_hm
        ${PRINTF} "%s" "
        The previous directories (0-$cd_maxhistory) are stored in the
        environment variables CD[0] - CD[$cd_maxhistory]
        Similarly the special directories S0 - $cd_maxspecial are in
        the environment variable CDS[0] - CDS[$cd_maxspecial]
        and may be accessed from the command line

        The default pathname for the -f and -u commands is $CDPath
        The default filename for the -f and -u commands is $CDFile

        Set the following environment variables:
            CDL_PROMPTLEN  - Set to the length of prompt you require.
                Prompt string is set to the right characters of the
                current directory.
                If not set then prompt is left unchanged
            CDL_PROMPT_PRE - Set to the string to prefix the prompt.
                Default is:
                    non-root:  \"\\[\\e[01;34m\\]\"  (sets colour to blue).
                    root:      \"\\[\\e[01;31m\\]\"  (sets colour to red).
            CDL_PROMPT_POST    - Set to the string to suffix the prompt.
                Default is:
                    non-root:  \"\\[\\e[00m\\]$\"
                                (resets colour and displays $).
                    root:      \"\\[\\e[00m\\]#\"
                                (resets colour and displays #).
            CDPath - Set the default path for the -f & -u options.
                     Default is home directory
            CDFile - Set the default filename for the -f & -u options.
                     Default is cdfile
        
"
    cd_version

}

cd_version ()
{
 printf "Version: ${VERSION_MAJOR}.${VERSION_MINOR} Date: ${VERSION_DATE}\n"
}

#
# Truncate right.
#
# params:
#   p1 - string
#   p2 - length to truncate to
#
# returns string in tcd
#
cd_right_trunc ()
{
    local tlen=${2}
    local plen=${#1}
    local str="${1}"
    local diff
    local filler="<--"
    if ${TEST} ${plen} -le ${tlen}
    then
        tcd="${str}"
    else
        let diff=${plen}-${tlen}
        elen=3
        if ${TEST} ${diff} -le 2
        then
            let elen=${diff}
        fi
        tlen=-${tlen}
        let tlen=${tlen}+${elen}
        tcd=${filler:0:elen}${str:tlen}
    fi
}

#
# Three versions of do history:
#    cd_dohistory  - packs history and specials side by side
#    cd_dohistoryH - Shows only hstory
#    cd_dohistoryS - Shows only specials
#
cd_dohistory ()
{
    cd_getrc
        ${PRINTF} "History:\n"
    local -i count=${cd_histcount}
    while ${TEST} ${count} -ge 0
    do
        cd_right_trunc "${CD[count]}" ${cd_lchar}
            ${PRINTF} "%2d %-${cd_lchar}.${cd_lchar}s " ${count} "${tcd}"

        cd_right_trunc "${CDS[count]}" ${cd_rchar}
            ${PRINTF} "S%d %-${cd_rchar}.${cd_rchar}s\n" ${count} "${tcd}"
        count=${count}-1
    done
}

cd_dohistoryH ()
{
    cd_getrc
        ${PRINTF} "History:\n"
        local -i count=${cd_maxhistory}
        while ${TEST} ${count} -ge 0
        do
          ${PRINTF} "${count} %-${cd_flchar}.${cd_flchar}s\n" ${CD[$count]}
          count=${count}-1
        done
}

cd_dohistoryS ()
{
    cd_getrc
        ${PRINTF} "Specials:\n"
        local -i count=${cd_maxspecial}
        while ${TEST} ${count} -ge 0
        do
          ${PRINTF} "S${count} %-${cd_flchar}.${cd_flchar}s\n" ${CDS[$count]}
          count=${count}-1
        done
}

cd_getrc ()
{
    cd_flchar=$(stty -a | awk -F \;
    '/rows/ { print $2 $3 }' | awk -F \  '{ print $4 }')
    if ${TEST} ${cd_flchar} -ne 0
    then
        cd_lchar=${cd_flchar}/2-5
        cd_rchar=${cd_flchar}/2-5
            cd_flchar=${cd_flchar}-5
    else
            cd_flchar=${FLCHAR:=75}
	    # cd_flchar is used for for the @s & @h history
            cd_lchar=${LCHAR:=35}
            cd_rchar=${RCHAR:=35}
    fi
}

cd_doselection ()
{
        local -i nm=0
        cd_doflag="TRUE"
        if ${TEST} "${CD_MODE}" = "PREV"
        then
                if ${TEST} -z "$cd_npwd"
                then
                        cd_npwd=0
                fi
        fi
        tm=$(echo "${cd_npwd}" | cut -b 1)
    if ${TEST} "${tm}" = "-"
    then
        pm=$(echo "${cd_npwd}" | cut -b 2)
        nm=$(echo "${cd_npwd}" | cut -d $pm -f2)
        case "${pm}" in
             a) cd_npwd=${cd_sugg[$nm]} ;;
             s) cd_npwd="${CDS[$nm]}" ;;
             S) cd_npwd="${CDS[$nm]}" ; CDS[$nm]=`pwd` ;;
             r) cd_npwd="$2" ; cd_specDir=$nm ; cd_doselection "$1" "$2";;
             R) cd_npwd="$2" ; CDS[$nm]=`pwd` ; cd_doselection "$1" "$2";;
        esac
    fi

    if ${TEST} "${cd_npwd}" != "." -a "${cd_npwd}" \
!= ".." -a "${cd_npwd}" -le ${cd_maxhistory} >>/dev/null 2>&1
    then
      cd_npwd=${CD[$cd_npwd]}
     else
       case "$cd_npwd" in
                @)  cd_dohistory ; cd_doflag="FALSE" ;;
               @h) cd_dohistoryH ; cd_doflag="FALSE" ;;
               @s) cd_dohistoryS ; cd_doflag="FALSE" ;;
               -h) cd_hm ; cd_doflag="FALSE" ;;
               -H) cd_Hm ; cd_doflag="FALSE" ;;
               -f) cd_fsave "SHOW" $2 ; cd_doflag="FALSE" ;;
               -u) cd_upload "SHOW" $2 ; cd_doflag="FALSE" ;;
               -F) cd_fsave "NOSHOW" $2 ; cd_doflag="FALSE" ;;
               -U) cd_upload "NOSHOW" $2 ; cd_doflag="FALSE" ;;
               -g) cd_npwd="$2" ;;
               -d) cd_chdefm 1; cd_doflag="FALSE" ;;
               -D) cd_chdefm 0; cd_doflag="FALSE" ;;
               -r) cd_npwd="$2" ; cd_specDir=0 ; cd_doselection "$1" "$2";;
               -R) cd_npwd="$2" ; CDS[0]=`pwd` ; cd_doselection "$1" "$2";;
               -s) cd_npwd="${CDS[0]}" ;;
               -S) cd_npwd="${CDS[0]}"  ; CDS[0]=`pwd` ;;
               -v) cd_version ; cd_doflag="FALSE";;
       esac
    fi
}

cd_chdefm ()
{
        if ${TEST} "${CD_MODE}" = "PREV"
        then
                CD_MODE=""
                if ${TEST} $1 -eq 1
                then
                        ${PRINTF} "${cd_mset}"
                fi
        else
                CD_MODE="PREV"
                if ${TEST} $1 -eq 1
                then
                        ${PRINTF} "${cd_mnset}"
                fi
        fi
}

cd_fsave ()
{
        local sfile=${CDPath}${2:-"$CDFile"}
        if ${TEST} "$1" = "SHOW"
        then
                ${PRINTF} "Saved to %s\n" $sfile
        fi
        ${RM} -f ${sfile}
        local -i count=0
        while ${TEST} ${count} -le ${cd_maxhistory}
        do
                echo "CD[$count]=\"${CD[$count]}\"" >> ${sfile}
                count=${count}+1
        done
        count=0
        while ${TEST} ${count} -le ${cd_maxspecial}
        do
                echo "CDS[$count]=\"${CDS[$count]}\"" >> ${sfile}
                count=${count}+1
        done
}

cd_upload ()
{
        local sfile=${CDPath}${2:-"$CDFile"}
        if ${TEST} "${1}" = "SHOW"
        then
                ${PRINTF} "Loading from %s\n" ${sfile}
        fi
        . ${sfile}
}

cd_new ()
{
    local -i count
    local -i choose=0

        cd_npwd="${1}"
        cd_specDir=-1
        cd_doselection "${1}" "${2}"

        if ${TEST} ${cd_doflag} = "TRUE"
        then
                if ${TEST} "${CD[0]}" != "`pwd`"
                then
                        count=$cd_maxhistory
                        while ${TEST} $count -gt 0
                        do
                                CD[$count]=${CD[$count-1]}
                                count=${count}-1
                        done
                        CD[0]=`pwd`
                fi
                command cd "${cd_npwd}" 2>/dev/null
        if ${TEST} $? -eq 1
        then
            ${PRINTF} "Unknown dir: %s\n" "${cd_npwd}"
            local -i ftflag=0
            for i in "${cd_npwd}"*
            do
                if ${TEST} -d "${i}"
                then
                    if ${TEST} ${ftflag} -eq 0
                    then
                        ${PRINTF} "Suggest:\n"
                        ftflag=1
                fi
                    ${PRINTF} "\t-a${choose} %s\n" "$i"
                                        cd_sugg[$choose]="${i}"
                    choose=${choose}+1
        fi
            done
        fi
        fi

        if ${TEST} ${cd_specDir} -ne -1
        then
                CDS[${cd_specDir}]=`pwd`
        fi

        if ${TEST} ! -z "${CDL_PROMPTLEN}"
        then
        cd_right_trunc "${PWD}" ${CDL_PROMPTLEN}
            cd_rp=${CDL_PROMPT_PRE}${tcd}${CDL_PROMPT_POST}
                export PS1="$(echo -ne ${cd_rp})"
        fi
}
#########################################################################
#                                                                       #
#                        Initialisation here                            #
#                                                                       #
#########################################################################
#
VERSION_MAJOR="1"
VERSION_MINOR="2.1"
VERSION_DATE="24-MAY-2003"
#
alias cd=cd_new
#
# Set up commands
RM=/bin/rm
TEST=test
PRINTF=printf              # Use builtin printf

#########################################################################
#                                                                       #
# Change this to modify the default pre- and post prompt strings.       #
# These only come into effect if CDL_PROMPTLEN is set.                  #
#                                                                       #
#########################################################################
if ${TEST} ${EUID} -eq 0
then
#   CDL_PROMPT_PRE=${CDL_PROMPT_PRE:="$HOSTNAME@"}
    CDL_PROMPT_PRE=${CDL_PROMPT_PRE:="\\[\\e[01;31m\\]"}  # Root is in red
    CDL_PROMPT_POST=${CDL_PROMPT_POST:="\\[\\e[00m\\]#"}
else
    CDL_PROMPT_PRE=${CDL_PROMPT_PRE:="\\[\\e[01;34m\\]"}  # Users in blue
    CDL_PROMPT_POST=${CDL_PROMPT_POST:="\\[\\e[00m\\]$"}
fi
#########################################################################
#
# cd_maxhistory defines the max number of history entries allowed.
typeset -i cd_maxhistory=50

#########################################################################
#
# cd_maxspecial defines the number of special entries.
typeset -i cd_maxspecial=9
#
#
#########################################################################
#
#  cd_histcount defines the number of entries displayed in
#+ the history command.
typeset -i cd_histcount=9
#
#########################################################################
export CDPath=${HOME}/
#  Change these to use a different                                      #
#+ default path and filename                                            #
export CDFile=${CDFILE:=cdfile}           # for the -u and -f commands  #
#
#########################################################################
                                                                        #
typeset -i cd_lchar cd_rchar cd_flchar
                        #  This is the number of chars to allow for the #
cd_flchar=${FLCHAR:=75} #+ cd_flchar is used for for the @s & @h history#

typeset -ax CD CDS
#
cd_mset="\n\tDefault mode is now set - entering cd with no parameters \
has the default action\n\tUse cd -d or -D for cd to go to \
previous directory with no parameters\n"
cd_mnset="\n\tNon-default mode is now set - entering cd with no \
parameters is the same as entering cd 0\n\tUse cd -d or \
-D to change default cd action\n"

# ==================================================================== #



: <<DOCUMENTATION

Written by Phil Braham. Realtime Software Pty Ltd.
Released under GNU license. Free to use. Please pass any modifications
or comments to the author Phil Braham:

realtime@mpx.com.au
=======================================================================

cdll is a replacement for cd and incorporates similar functionality to
the bash pushd and popd commands but is independent of them.

This version of cdll has been tested on Linux using Bash. It will work
on most Linux versions but will probably not work on other shells without
modification.

Introduction
============

cdll allows easy moving about between directories. When changing to a new
directory the current one is automatically put onto a stack. By default
50 entries are kept, but this is configurable. Special directories can be
kept for easy access - by default up to 10, but this is configurable. The
most recent stack entries and the special entries can be easily viewed.

The directory stack and special entries can be saved to, and loaded from,
a file. This allows them to be set up on login, saved before logging out
or changed when moving project to project.

In addition, cdll provides a flexible command prompt facility that allows,
for example, a directory name in colour that is truncated from the left
if it gets too long.


Setting up cdll
===============

Copy cdll to either your local home directory or a central directory
such as /usr/bin (this will require root access).

Copy the file cdfile to your home directory. It will require read and
write access. This a default file that contains a directory stack and
special entries.

To replace the cd command you must add commands to your login script.
The login script is one or more of:

    /etc/profile
    ~/.bash_profile
    ~/.bash_login
    ~/.profile
    ~/.bashrc
    /etc/bash.bashrc.local
    
To setup your login, ~/.bashrc is recommended, for global (and root) setup
add the commands to /etc/bash.bashrc.local
    
To set up on login, add the command:
    . <dir>/cdll
For example if cdll is in your local home directory:
    . ~/cdll
If in /usr/bin then:
    . /usr/bin/cdll

If you want to use this instead of the buitin cd command then add:
    alias cd='cd_new'
We would also recommend the following commands:
    alias @='cd_new @'
    cd -U
    cd -D

If you want to use cdll's prompt facilty then add the following:
    CDL_PROMPTLEN=nn
Where nn is a number described below. Initially 99 would be suitable
number.

Thus the script looks something like this:

    ######################################################################
    # CD Setup
    ######################################################################
    CDL_PROMPTLEN=21        # Allow a prompt length of up to 21 characters
    . /usr/bin/cdll         # Initialise cdll
    alias cd='cd_new'       # Replace the built in cd command
    alias @='cd_new @'      # Allow @ at the prompt to display history
    cd -U                   # Upload directories
    cd -D                   # Set default action to non-posix
    ######################################################################

The full meaning of these commands will become clear later.

There are a couple of caveats. If another program changes the directory
without calling cdll, then the directory won't be put on the stack and
also if the prompt facility is used then this will not be updated. Two
programs that can do this are pushd and popd. To update the prompt and
stack simply enter:

    cd .
    
Note that if the previous entry on the stack is the current directory
then the stack is not updated.

Usage
=====  
cd [dir] [0-9] [@[s|h] [-g <dir>] [-d] [-D] [-r<n>]
   [dir|0-9] [-R<n>] [<dir>|0-9] [-s<n>] [-S<n>]
   [-u] [-U] [-f] [-F] [-h] [-H] [-v]

    <dir>       Go to directory
    0-n         Goto previous directory (0 is previous,
                1 is last but 1, etc.)
                n is up to max history (default is 50)
    @           List history and special entries (Usually available as $ @)
    @h          List history entries
    @s          List special entries
    -g [<dir>]  Go to literal name (bypass special names)
                This is to allow access to dirs called '0','1','-h' etc
    -d          Change default action - verbose. (See note)
    -D          Change default action - silent. (See note)
    -s<n>       Go to the special entry <n>
    -S<n>       Go to the special entry <n>
                      and replace it with the current dir
    -r<n> [<dir>] Go to directory <dir>
                              and then put it on special entry <n>
    -R<n> [<dir>] Go to directory <dir>
                              and put current dir on special entry <n>
    -a<n>       Alternative suggested directory. See note below.
    -f [<file>] File entries to <file>.
    -u [<file>] Update entries from <file>.
                If no filename supplied then default file (~/cdfile) is used
                -F and -U are silent versions
    -v          Print version number
    -h          Help
    -H          Detailed help



Examples
========

These examples assume non-default mode is set (that is, cd with no
parameters will go to the most recent stack directory), that aliases
have been set up for cd and @ as described above and that cd's prompt
facility is active and the prompt length is 21 characters.

    /home/phil$ @
    # List the entries with the @
    History:
    # Output of the @ command
    .....
    # Skipped these entries for brevity
    1 /home/phil/ummdev               S1 /home/phil/perl
    # Most recent two history entries
    0 /home/phil/perl/eg              S0 /home/phil/umm/ummdev
    # and two special entries are shown
    
    /home/phil$ cd /home/phil/utils/Cdll
    # Now change directories
    /home/phil/utils/Cdll$ @
    # Prompt reflects the directory.
    History:
    # New history
    .....   
    1 /home/phil/perl/eg              S1 /home/phil/perl
    # History entry 0 has moved to 1
    0 /home/phil                      S0 /home/phil/umm/ummdev
    # and the most recent has entered
       
To go to a history entry:

    /home/phil/utils/Cdll$ cd 1
    # Go to history entry 1.
    /home/phil/perl/eg$
    # Current directory is now what was 1
    
To go to a special entry:

    /home/phil/perl/eg$ cd -s1
    # Go to special entry 1
    /home/phil/umm/ummdev$
    # Current directory is S1

To go to a directory called, for example, 1:

    /home/phil$ cd -g 1
    # -g ignores the special meaning of 1
    /home/phil/1$
    
To put current directory on the special list as S1:
    cd -r1 .        #  OR
    cd -R1 .        #  These have the same effect if the directory is
                    #+ . (the current directory)

To go to a directory and add it as a special  
  The directory for -r<n> or -R<n> may be a number.
  For example:
        $ cd -r3 4  Go to history entry 4 and put it on special entry 3
        $ cd -R3 4  Put current dir on the special entry 3 and go to
                    history entry 4
        $ cd -s3    Go to special entry 3

    Note that commands R,r,S and s may be used without a number and
    refer to 0:
        $ cd -s     Go to special entry 0
        $ cd -S     Go to special entry 0 and make special entry 0
                    current dir
        $ cd -r 1   Go to history entry 1 and put it on special entry 0
        $ cd -r     Go to history entry 0 and put it on special entry 0


    Alternative suggested directories:

    If a directory is not found, then CD will suggest any
    possibilities. These are directories starting with the same letters
    and if any are found they are listed prefixed with -a<n>
    where <n> is a number. It's possible to go to the directory
    by entering cd -a<n> on the command line.

        Use cd -d or -D to change default cd action. cd -H will show
        current action.

        The history entries (0-n) are stored in the environment variables
        CD[0] - CD[n]
        Similarly the special directories S0 - 9 are in the environment
        variable CDS[0] - CDS[9]
        and may be accessed from the command line, for example:
        
            ls -l ${CDS[3]}
            cat ${CD[8]}/file.txt

        The default pathname for the -f and -u commands is ~
        The default filename for the -f and -u commands is cdfile


Configuration
=============

    The following environment variables can be set:
    
        CDL_PROMPTLEN  - Set to the length of prompt you require.
            Prompt string is set to the right characters of the current
            directory. If not set, then prompt is left unchanged. Note
            that this is the number of characters that the directory is
            shortened to, not the total characters in the prompt.

            CDL_PROMPT_PRE - Set to the string to prefix the prompt.
                Default is:
                    non-root:  "\\[\\e[01;34m\\]"  (sets colour to blue).
                    root:      "\\[\\e[01;31m\\]"  (sets colour to red).

            CDL_PROMPT_POST    - Set to the string to suffix the prompt.
                Default is:
                    non-root:  "\\[\\e[00m\\]$"
                               (resets colour and displays $).
                    root:      "\\[\\e[00m\\]#"
                               (resets colour and displays #).

        Note:
            CDL_PROMPT_PRE & _POST only t

        CDPath - Set the default path for the -f & -u options.
                 Default is home directory
        CDFile - Set the default filename for the -f & -u options.
                 Default is cdfile


    There are three variables defined in the file cdll which control the
    number of entries stored or displayed. They are in the section labeled
    'Initialisation here' towards the end of the file.

        cd_maxhistory       - The number of history entries stored.
                              Default is 50.
        cd_maxspecial       - The number of special entries allowed.
                              Default is 9.
        cd_histcount        - The number of history and special entries
                              displayed. Default is 9.

    Note that cd_maxspecial should be >= cd_histcount to avoid displaying
    special entries that can't be set.


Version: 1.2.1 Date: 24-MAY-2003

DOCUMENTATION

Example A-36. A soundcard setup script

#!/bin/bash
# soundcard-on.sh

#  Script author: Mkarcher
#  http://www.thinkwiki.org/wiki  ...
#  /Script_for_configuring_the_CS4239_sound_chip_in_PnP_mode
#  ABS Guide author made minor changes and added comments.
#  Couldn't contact script author to ask for permission to use, but ...
#+ the script was released under the FDL,
#+ so its use here should be both legal and ethical.

#  Sound-via-pnp-script for Thinkpad 600E
#+ and possibly other computers with onboard CS4239/CS4610
#+ that do not work with the PCI driver
#+ and are not recognized by the PnP code of snd-cs4236.
#  Also for some 770-series Thinkpads, such as the 770x.
#  Run as root user, of course.
#
#  These are old and very obsolete laptop computers,
#+ but this particular script is very instructive,
#+ as it shows how to set up and hack device files.



#  Search for sound card pnp device:

for dev in /sys/bus/pnp/devices/*
do
  grep CSC0100 $dev/id > /dev/null && WSSDEV=$dev
  grep CSC0110 $dev/id > /dev/null && CTLDEV=$dev
done
# On 770x:
# WSSDEV = /sys/bus/pnp/devices/00:07
# CTLDEV = /sys/bus/pnp/devices/00:06
# These are symbolic links to /sys/devices/pnp0/ ...


#  Activate devices:
#  Thinkpad boots with devices disabled unless "fast boot" is turned off
#+ (in BIOS).

echo activate > $WSSDEV/resources
echo activate > $CTLDEV/resources


# Parse resource settings.

{ read # Discard "state = active" (see below).
  read bla port1
  read bla port2
  read bla port3
  read bla irq
  read bla dma1
  read bla dma2
 # The "bla's" are labels in the first field: "io," "state," etc.
 # These are discarded.

 #  Hack: with PnPBIOS: ports are: port1: WSS, port2:
 #+ OPL, port3: sb (unneeded)
 #       with ACPI-PnP:ports are: port1: OPL, port2: sb, port3: WSS
 #  (ACPI bios seems to be wrong here, the PnP-card-code in snd-cs4236.c
 #+  uses the PnPBIOS port order)
 #  Detect port order using the fixed OPL port as reference.
  if [ ${port2%%-*} = 0x388 ]
 #            ^^^^  Strip out everything following hyphen in port address.
 #                  So, if port1 is 0x530-0x537
 #+                 we're left with 0x530 -- the start address of the port.
 then
   # PnPBIOS: usual order
   port=${port1%%-*}
   oplport=${port2%%-*}
 else
   # ACPI: mixed-up order
   port=${port3%%-*}
   oplport=${port1%%-*}
 fi
 } < $WSSDEV/resources
# To see what's going on here:
# ---------------------------
#   cat /sys/devices/pnp0/00:07/resources
#
#   state = active
#   io 0x530-0x537
#   io 0x388-0x38b
#   io 0x220-0x233
#   irq 5
#   dma 1
#   dma 0
#   ^^^   "bla" labels in first field (discarded). 


{ read # Discard first line, as above.
  read bla port1
  cport=${port1%%-*}
  #            ^^^^
  # Just want _start_ address of port.
} < $CTLDEV/resources


# Load the module:

modprobe --ignore-install snd-cs4236 port=$port cport=$cport\
fm_port=$oplport irq=$irq dma1=$dma1 dma2=$dma2 isapnp=0 index=0
# See the modprobe manpage.

exit $?

Example A-37. Locating split paragraphs in a text file

#!/bin/bash
# find-splitpara.sh
#  Finds split paragraphs in a text file,
#+ and tags the line numbers.


ARGCOUNT=1       # Expect one arg.
E_WRONGARGS=65

file="$1"        # Target filename.
lineno=1         # Line number. Start at 1.
Flag=0           # Blank line flag.

if [ $# -ne "$ARGCOUNT" ]
then
  echo "Usage: `basename $0` FILENAME"
  exit $E_WRONGARGS
fi  

file_read ()     # Scan file for pattern, then print line.
{
while read line
do

  if [[ "$line" =~ ^[a-z] && $Flag -eq 1 ]]
     then  # Line begins with lc character, following blank line.
     echo -n "$lineno::   "
     echo "$line"
  fi


  if [[ "$line" =~ "^$" ]]
     then     #  If blank line,
     Flag=1   #+ set flag.
  else
     Flag=0
  fi

  ((lineno++))

done
} < $file  # Redirect file into function's stdin.

file_read


exit $?


# ----------------------------------------------------------------
This is line one of an example paragraph, bla, bla, bla.
This is line two, and line three should follow on next line, but

there is a blank line separating the two parts of the paragraph.
# ----------------------------------------------------------------

Running this script on a file containing the above paragraph
yields:

4::   there is a blank line separating the two parts of the paragraph.


There will be additional output for all the other split paragraphs
in the target file.

Example A-38. Insertion sort

#!/bin/bash
# insertion-sort.bash: Insertion sort implementation in Bash
#                      Heavy use of Bash array features:
#+                     (string) slicing, merging, etc
# URL: http://www.lugmen.org.ar/~jjo/jjotip/insertion-sort.bash.d
#+          /insertion-sort.bash.sh
#
# Author: JuanJo Ciarlante <jjo@irrigacion.gov.ar>
# Lightly reformatted by ABS Guide author.
# License: GPLv2
# Used in ABS Guide with author's permission (thanks!).
#
# Test with:   ./insertion-sort.bash -t
# Or:          bash insertion-sort.bash -t
# The following *doesn't* work:
#              sh insertion-sort.bash -t
#  Why not? Hint: which Bash-specific features are disabled
#+ when running a script by 'sh script.sh'?
#
: ${DEBUG:=0}  # Debug, override with:  DEBUG=1 ./scriptname . . .
# Parameter substitution -- set DEBUG to 0 if not previously set.

# Global array: "list"
typeset -a list
# Load whitespace-separated numbers from stdin.
if [ "$1" = "-t" ]; then
DEBUG=1
        read -a list < <( od -Ad -w24 -t u2 /dev/urandom ) # Random list.
#                    ^ ^  process substition
else
        read -a list
fi
numelem=${#list[*]}

#  Shows the list, marking the element whose index is $1
#+ by surrounding it with the two chars passed as $2.
#  Whole line prefixed with $3.
showlist()
  {
  echo "$3"${list[@]:0:$1} ${2:0:1}${list[$1]}${2:1:1} ${list[@]:$1+1};
  }

# Loop _pivot_ -- from second element to end of list.
for(( i=1; i<numelem; i++ )) do
        ((DEBUG))&&showlist i "[]" " "
        # From current _pivot_, back to first element.
        for(( j=i; j; j-- )) do
                # Search for the 1st elem. less than current "pivot" . . .
                [[ "${list[j-1]}" -le "${list[i]}" ]] && break
        done
	(( i==j )) && continue ## No insertion was needed for this element.
	# . . . Move list[i] (pivot) to the left of list[j]:
        list=(${list[@]:0:j} ${list[i]} ${list[j]}\
	#         {0,j-1}        {i}       {j}
              ${list[@]:j+1:i-(j+1)} ${list[@]:i+1})
	#         {j+1,i-1}              {i+1,last}
	((DEBUG))&&showlist j "<>" "*"
done


echo
echo  "------"
echo $'Result:\n'${list[@]}

exit $?

Example A-39. Standard Deviation

#!/bin/bash
# sd.sh: Standard Deviation

#  The Standard Deviation indicates how consistent a set of data is.
#  It shows to what extent the individual data points deviate from the
#+ arithmetic mean, i.e., how much they "bounce around" (or cluster).
#  It is essentially the average deviation-distance of the
#+ data points from the mean.

# =========================================================== #
#    To calculate the Standard Deviation:
#
# 1  Find the arithmetic mean (average) of all the data points.
# 2  Subtract each data point from the arithmetic mean,
#    and square that difference.
# 3  Add all of the individual difference-squares in # 2.
# 4  Divide the sum in # 3 by the number of data points.
#    This is known as the "variance."
# 5  The square root of # 4 gives the Standard Deviation.
# =========================================================== #

count=0         # Number of data points; global.
SC=9            # Scale to be used by bc. Nine decimal places.
E_DATAFILE=90   # Data file error.

# ----------------- Set data file ---------------------
if [ ! -z "$1" ]  # Specify filename as cmd-line arg?
then
  datafile="$1" #  ASCII text file,
else            #+ one (numerical) data point per line!
  datafile=sample.dat
fi              #  See example data file, below.

if [ ! -e "$datafile" ]
then
  echo "\""$datafile"\" does not exist!"
  exit $E_DATAFILE
fi
# -----------------------------------------------------


arith_mean ()
{
  local rt=0         # Running total.
  local am=0         # Arithmetic mean.
  local ct=0         # Number of data points.

  while read value   # Read one data point at a time.
  do
    rt=$(echo "scale=$SC; $rt + $value" | bc)
    (( ct++ ))
  done

  am=$(echo "scale=$SC; $rt / $ct" | bc)

  echo $am; return $ct   # This function "returns" TWO values!
  #  Caution: This little trick will not work if $ct > 255!
  #  To handle a larger number of data points,
  #+ simply comment out the "return $ct" above.
} <"$datafile"   # Feed in data file.

sd ()
{
  mean1=$1  # Arithmetic mean (passed to function).
  n=$2      # How many data points.
  sum2=0    # Sum of squared differences ("variance").
  avg2=0    # Average of $sum2.
  sdev=0    # Standard Deviation.

  while read value   # Read one line at a time.
  do
    diff=$(echo "scale=$SC; $mean1 - $value" | bc)
    # Difference between arith. mean and data point.
    dif2=$(echo "scale=$SC; $diff * $diff" | bc) # Squared.
    sum2=$(echo "scale=$SC; $sum2 + $dif2" | bc) # Sum of squares.
  done

    avg2=$(echo "scale=$SC; $sum2 / $n" | bc)  # Avg. of sum of squares.
    sdev=$(echo "scale=$SC; sqrt($avg2)" | bc) # Square root =
    echo $sdev                                 # Standard Deviation.

} <"$datafile"   # Rewinds data file.


# ======================================================= #
mean=$(arith_mean); count=$?   # Two returns from function!
std_dev=$(sd $mean $count)

echo
echo "Number of data points in \""$datafile"\" = $count"
echo "Arithmetic mean (average) = $mean"
echo "Standard Deviation = $std_dev"
echo
# ======================================================= #

exit

#  This script could stand some drastic streamlining,
#+ but not at the cost of reduced legibility, please.


# ++++++++++++++++++++++++++++++++++++++++ #
# A sample data file (sample1.dat):

# 18.35
# 19.0
# 18.88
# 18.91
# 18.64


# $ sh sd.sh sample1.dat

# Number of data points in "sample1.dat" = 5
# Arithmetic mean (average) = 18.756000000
# Standard Deviation = .235338054
# ++++++++++++++++++++++++++++++++++++++++ #

Example A-40. A pad file generator for shareware authors

#!/bin/bash
# pad.sh

#######################################################
#               PAD (xml) file creator
#+ Written by Mendel Cooper <thegrendel.abs@gmail.com>.
#+ Released to the Public Domain.
#
#  Generates a "PAD" descriptor file for shareware
#+ packages, according to the specifications
#+ of the ASP.
#  http://www.asp-shareware.org/pad
#######################################################


# Accepts (optional) save filename as a command-line argument.
if [ -n "$1" ]
then
  savefile=$1
else
  savefile=save_file.xml               # Default save_file name.
fi  


# ===== PAD file headers =====
HDR1="<?xml version=\"1.0\" encoding=\"Windows-1252\" ?>"
HDR2="<XML_DIZ_INFO>"
HDR3="<MASTER_PAD_VERSION_INFO>"
HDR4="\t<MASTER_PAD_VERSION>1.15</MASTER_PAD_VERSION>"
HDR5="\t<MASTER_PAD_INFO>Portable Application Description, or PAD
for short, is a data set that is used by shareware authors to
disseminate information to anyone interested in their software products.
To find out more go to http://www.asp-shareware.org/pad</MASTER_PAD_INFO>"
HDR6="</MASTER_PAD_VERSION_INFO>"
# ============================


fill_in ()
{
  if [ -z "$2" ]
  then
    echo -n "$1? "     # Get user input.
  else
    echo -n "$1 $2? "  # Additional query?
  fi  

  read var             # May paste to fill in field.
                       # This shows how flexible "read" can be.

  if [ -z "$var" ]
  then
    echo -e "\t\t<$1 />" >>$savefile    # Indent with 2 tabs.
    return
  else
    echo -e "\t\t<$1>$var</$1>" >>$savefile
    return ${#var}     # Return length of input string.
  fi
}    

check_field_length ()  # Check length of program description fields.
{
  # $1 = maximum field length
  # $2 = actual field length
  if [ "$2" -gt "$1" ]
  then
    echo "Warning: Maximum field length of $1 characters exceeded!"
  fi
}  

clear                  # Clear screen.
echo "PAD File Creator"
echo "--- ---- -------"
echo

# Write File Headers to file.
echo $HDR1 >$savefile
echo $HDR2 >>$savefile
echo $HDR3 >>$savefile
echo -e $HDR4 >>$savefile
echo -e $HDR5 >>$savefile
echo $HDR6 >>$savefile


# Company_Info
echo "COMPANY INFO"
CO_HDR="Company_Info"
echo "<$CO_HDR>" >>$savefile

fill_in Company_Name
fill_in Address_1
fill_in Address_2
fill_in City_Town 
fill_in State_Province
fill_in Zip_Postal_Code
fill_in Country

# If applicable:
# fill_in ASP_Member "[Y/N]"
# fill_in ASP_Member_Number
# fill_in ESC_Member "[Y/N]"

fill_in Company_WebSite_URL

clear   # Clear screen between sections.

   # Contact_Info
echo "CONTACT INFO"
CONTACT_HDR="Contact_Info"
echo "<$CONTACT_HDR>" >>$savefile
fill_in Author_First_Name
fill_in Author_Last_Name
fill_in Author_Email
fill_in Contact_First_Name
fill_in Contact_Last_Name
fill_in Contact_Email
echo -e "\t</$CONTACT_HDR>" >>$savefile
   # END Contact_Info

clear

   # Support_Info
echo "SUPPORT INFO"
SUPPORT_HDR="Support_Info"
echo "<$SUPPORT_HDR>" >>$savefile
fill_in Sales_Email
fill_in Support_Email
fill_in General_Email
fill_in Sales_Phone
fill_in Support_Phone
fill_in General_Phone
fill_in Fax_Phone
echo -e "\t</$SUPPORT_HDR>" >>$savefile
   # END Support_Info

echo "</$CO_HDR>" >>$savefile
# END Company_Info

clear

# Program_Info 
echo "PROGRAM INFO"
PROGRAM_HDR="Program_Info"
echo "<$PROGRAM_HDR>" >>$savefile
fill_in Program_Name
fill_in Program_Version
fill_in Program_Release_Month
fill_in Program_Release_Day
fill_in Program_Release_Year
fill_in Program_Cost_Dollars
fill_in Program_Cost_Other
fill_in Program_Type "[Shareware/Freeware/GPL]"
fill_in Program_Release_Status "[Beta, Major Upgrade, etc.]"
fill_in Program_Install_Support
fill_in Program_OS_Support "[Win9x/Win2k/Linux/etc.]"
fill_in Program_Language "[English/Spanish/etc.]"

echo; echo

  # File_Info 
echo "FILE INFO"
FILEINFO_HDR="File_Info"
echo "<$FILEINFO_HDR>" >>$savefile
fill_in Filename_Versioned
fill_in Filename_Previous
fill_in Filename_Generic
fill_in Filename_Long
fill_in File_Size_Bytes
fill_in File_Size_K
fill_in File_Size_MB
echo -e "\t</$FILEINFO_HDR>" >>$savefile
  # END File_Info 

clear

  # Expire_Info 
echo "EXPIRE INFO"
EXPIRE_HDR="Expire_Info"
echo "<$EXPIRE_HDR>" >>$savefile
fill_in Has_Expire_Info "Y/N"
fill_in Expire_Count
fill_in Expire_Based_On
fill_in Expire_Other_Info
fill_in Expire_Month
fill_in Expire_Day
fill_in Expire_Year
echo -e "\t</$EXPIRE_HDR>" >>$savefile
  # END Expire_Info 

clear

  # More Program_Info
echo "ADDITIONAL PROGRAM INFO"
fill_in Program_Change_Info
fill_in Program_Specific_Category
fill_in Program_Categories
fill_in Includes_JAVA_VM "[Y/N]"
fill_in Includes_VB_Runtime "[Y/N]"
fill_in Includes_DirectX "[Y/N]"
  # END More Program_Info

echo "</$PROGRAM_HDR>" >>$savefile
# END Program_Info 

clear

# Program Description
echo "PROGRAM DESCRIPTIONS"
PROGDESC_HDR="Program_Descriptions"
echo "<$PROGDESC_HDR>" >>$savefile

LANG="English"
echo "<$LANG>" >>$savefile

fill_in Keywords "[comma + space separated]"
echo
echo "45, 80, 250, 450, 2000 word program descriptions"
echo "(may cut and paste into field)"
#  It would be highly appropriate to compose the following
#+ "Char_Desc" fields with a text editor,
#+ then cut-and-paste the text into the answer fields.
echo
echo "              |---------------45 characters---------------|"
fill_in Char_Desc_45
check_field_length 45 "$?"
echo
fill_in Char_Desc_80
check_field_length 80 "$?"

fill_in Char_Desc_250
check_field_length 250 "$?"

fill_in Char_Desc_450
fill_in Char_Desc_2000

echo "</$LANG>" >>$savefile
echo "</$PROGDESC_HDR>" >>$savefile
# END Program Description

clear
echo "Done."; echo; echo
echo "Save file is:  \""$savefile"\""

exit 0

Example A-41. A man page editor

#!/bin/bash
# maned.sh
# A rudimentary man page editor

# Version: 0.1 (Alpha, probably buggy)
# Author: Mendel Cooper <thegrendel.abs@gmail.com>
# Reldate: 16 June 2008
# License: GPL3


savefile=      # Global, used in multiple functions.
E_NOINPUT=90   # User input missing (error). May or may not be critical.

# =========== Markup Tags ============ #
TopHeader=".TH"
NameHeader=".SH NAME"
SyntaxHeader=".SH SYNTAX"
SynopsisHeader=".SH SYNOPSIS"
InstallationHeader=".SH INSTALLATION"
DescHeader=".SH DESCRIPTION"
OptHeader=".SH OPTIONS"
FilesHeader=".SH FILES"
EnvHeader=".SH ENVIRONMENT"
AuthHeader=".SH AUTHOR"
BugsHeader=".SH BUGS"
SeeAlsoHeader=".SH SEE ALSO"
BOLD=".B"
# Add more tags, as needed.
# See groff docs for markup meanings.
# ==================================== #

start ()
{
clear                  # Clear screen.
echo "ManEd"
echo "-----"
echo
echo "Simple man page creator"
echo "Author: Mendel Cooper"
echo; echo; echo
}

progname ()
{
  echo -n "Program name? "
  read name

  echo -n "Manpage section? [Hit RETURN for default (\"1\") ]  "
  read section
  if [ -z "$section" ]
  then
    section=1   # Most man pages are in section 1.
  fi

  if [ -n "$name" ]
  then
    savefile=""$name"."$section""       #  Filename suffix = section.
    echo -n "$1 " >>$savefile
    name1=$(echo "$name" | tr a-z A-Z)  #  Change to uppercase,
                                        #+ per man page convention.
    echo -n "$name1" >>$savefile
  else
    echo "Error! No input."             # Mandatory input.
    exit $E_NOINPUT                     # Critical!
  fi

  echo -n "  \"$section\"">>$savefile   # Append, always append.

  echo -n "Version? "
  read ver
  echo -n " \"Version $ver \"">>$savefile
  echo >>$savefile

  echo -n "Short description [0 - 5 words]? "
  read sdesc
  echo "$NameHeader">>$savefile
  echo ""$BOLD" "$name"">>$savefile
  echo "\- "$sdesc"">>$savefile

}

fill_in ()
{ # This function more or less copied from "pad.sh" script.
  echo -n "$2? "       # Get user input.
  read var             # May paste (a single line only!) to fill in field.

  if [ -n "$var" ]
  then
    echo "$1 " >>$savefile
    echo -n "$var" >>$savefile
  else                 # Don't append empty field to file.
    return $E_NOINPUT  # Not critical here.
  fi

  echo >>$savefile

}    


end ()
{
clear
echo -n "Would you like to view the saved man page (y/n)? "
read ans
if [ "$ans" = "n" -o "$ans" = "N" ]; then exit; fi
exec less "$savefile"  #  Exit script and hand off control to "less" ...
                       #+ ... which formats for viewing man page source.
}


# ---------------------------------------- #
start
progname "$TopHeader"
fill_in "$SynopsisHeader" "Synopsis"
fill_in "$DescHeader" "Long description"
# May paste in *single line* of text.
fill_in "$OptHeader" "Options"
fill_in "$FilesHeader" "Files"
fill_in "$AuthHeader" "Author"
fill_in "$BugsHeader" "Bugs"
fill_in "$SeeAlsoHeader" "See also"
# fill_in "$OtherHeader" ... as necessary.
end    # ... exit not needed.
# ---------------------------------------- #

#  Note that the generated man page will usually
#+ require manual fine-tuning with a text editor.
#  However, it's a distinct improvement upon
#+ writing man source from scratch
#+ or even editing a blank man page template.

#  The main deficiency of the script is that it permits
#+ pasting only a single text line into the input fields.
#  This may be a long, cobbled-together line, which groff
#  will automatically wrap and hyphenate.
#  However, if you want multiple (newline-separated) paragraphs,
#+ these must be inserted by manual text editing on the
#+ script-generated man page.
#  Exercise (difficult): Fix this!

#  This script is not nearly as elaborate as the
#+ full-featured "manedit" package (http://wolfpack.twu.net),
#+ but it's much easier to use.

Example A-42. Petals Around the Rose

#!/bin/bash -i
# petals.sh

#########################################################################
# Petals Around the Rose                                                #
#                                                                       #
# Version 0.1 Created by Serghey Rodin                                  #
# Version 0.2 Modded by ABS Guide Author                                #
#                                                                       #
# License: GPL3                                                         #
# Used in ABS Guide with permission.                                    #
# ##################################################################### #

hits=0      # Correct guesses.
WIN=6       # Mastered the game.
ALMOST=5    # One short of mastery.
EXIT=exit   # Give up early?

RANDOM=$$   # Seeds the random number generator from PID of script.


# Bones (ASCII graphics for dice)
bone1[1]="|         |"
bone1[2]="|       o |"
bone1[3]="|       o |"
bone1[4]="| o     o |"
bone1[5]="| o     o |"
bone1[6]="| o     o |"
bone2[1]="|    o    |"
bone2[2]="|         |"
bone2[3]="|    o    |"
bone2[4]="|         |"
bone2[5]="|    o    |"
bone2[6]="| o     o |"
bone3[1]="|         |"
bone3[2]="| o       |"
bone3[3]="| o       |"
bone3[4]="| o     o |"
bone3[5]="| o     o |"
bone3[6]="| o     o |"
bone="+---------+"



# Functions

instructions () {

  clear
  echo -n "Do you need instructions? (y/n) "; read ans
  if [ "$ans" = "y" -o "$ans" = "Y" ]; then
    clear
    echo -e '\E[34;47m'  # Blue type.

#  "cat document"
    cat <<INSTRUCTIONSZZZ
The name of the game is Petals Around the Rose,
and that name is significant.
Five dice will roll and you must guess the "answer" for each roll.
It will be zero or an even number.
After your guess, you will be told the answer for the roll, but . . .
that's ALL the information you will get.

Six consecutive correct guesses admits you to the
Fellowship of the Rose.
INSTRUCTIONSZZZ

    echo -e "\033[0m"    # Turn off blue.
    else clear
  fi

}


fortune ()
{
  RANGE=7
  FLOOR=0
  number=0
  while [ "$number" -le $FLOOR ]
  do
    number=$RANDOM
    let "number %= $RANGE"   # 1 - 6.
  done

  return $number
}



throw () { # Calculate each individual die.
  fortune; B1=$?
  fortune; B2=$?
  fortune; B3=$?
  fortune; B4=$?
  fortune; B5=$?

  calc () { # Function embedded within a function!
    case "$1" in
       3   ) rose=2;;
       5   ) rose=4;;
       *   ) rose=0;;
    esac    # Simplified algorithm.
            # Doesn't really get to the heart of the matter.
    return $rose
  }

  answer=0
  calc "$B1"; answer=$(expr $answer + $(echo $?))
  calc "$B2"; answer=$(expr $answer + $(echo $?))
  calc "$B3"; answer=$(expr $answer + $(echo $?))
  calc "$B4"; answer=$(expr $answer + $(echo $?))
  calc "$B5"; answer=$(expr $answer + $(echo $?))
}



game ()
{ # Generate graphic display of dice throw.
  throw
    echo -e "\033[1m"    # Bold.
  echo -e "\n"
  echo -e "$bone\t$bone\t$bone\t$bone\t$bone"
  echo -e \
 "${bone1[$B1]}\t${bone1[$B2]}\t${bone1[$B3]}\t${bone1[$B4]}\t${bone1[$B5]}"
  echo -e \
 "${bone2[$B1]}\t${bone2[$B2]}\t${bone2[$B3]}\t${bone2[$B4]}\t${bone2[$B5]}"
  echo -e \
 "${bone3[$B1]}\t${bone3[$B2]}\t${bone3[$B3]}\t${bone3[$B4]}\t${bone3[$B5]}"
  echo -e "$bone\t$bone\t$bone\t$bone\t$bone"
  echo -e "\n\n\t\t"
    echo -e "\033[0m"    # Turn off bold.
  echo -n "There are how many petals around the rose? "
}



# ============================================================== #

instructions

while [ "$petal" != "$EXIT" ]    # Main loop.
do
  game
  read petal
  echo "$petal" | grep [0-9] >/dev/null  # Filter response for digit.
                                         # Otherwise just roll dice again.
  if [ "$?" -eq 0 ]   # If-loop #1.
  then
    if [ "$petal" == "$answer" ]; then    # If-loop #2.
    	echo -e "\nCorrect. There are $petal petals around the rose.\n"
        (( hits++ ))

        if [ "$hits" -eq "$WIN" ]; then   # If-loop #3.
          echo -e '\E[31;47m'  # Red type.
          echo -e "\033[1m"    # Bold.
          echo "You have unraveled the mystery of the Rose Petals!"
          echo "Welcome to the Fellowship of the Rose!!!"
          echo "(You are herewith sworn to secrecy.)"; echo
          echo -e "\033[0m"    # Turn off red & bold.
          break                # Exit!
        else echo "You have $hits correct so far."; echo

        if [ "$hits" -eq "$ALMOST" ]; then
          echo "Just one more gets you to the heart of the mystery!"; echo
        fi

      fi                                  # Close if-loop #3.

    else
      echo -e "\nWrong. There are $answer petals around the rose.\n"
      hits=0   # Reset number of correct guesses.
    fi                                    # Close if-loop #2.

    echo -n "Hit ENTER for the next roll, or type \"exit\" to end. "
    read
    if [ "$REPLY" = "$EXIT" ]; then exit
    fi

  fi                  # Close if-loop #1.

  clear
done                  # End of main (while) loop.

###

exit $?

# Resources:
# ---------
# 1) http://en.wikipedia.org/wiki/Petals_Around_the_Rose
#    (Wikipedia entry.)
# 2) http://www.borrett.id.au/computing/petals-bg.htm
#    (How Bill Gates coped with the Petals Around the Rose challenge.)

Example A-43. Quacky: a Perquackey-type word game

#!/bin/bash
# qky.sh

##############################################################
# QUACKEY: a somewhat simplified version of Perquackey [TM]. #
#                                                            #
# Author: Mendel Cooper  <thegrendel.abs@gmail.com>          #
# version 0.1.02      03 May, 2008                           #
# License: GPL3                                              #
##############################################################

WLIST=/usr/share/dict/word.lst
#                     ^^^^^^^^  Word list file found here.
#  ASCII word list, one word per line, UNIX format.
#  A suggested list is the script author's "yawl" word list package.
#  http://bash.neuralshortciruit.com/yawl-0.3.2.tar.gz
#    or
#  http://ibiblio.org/pub/Linux/libs/yawl-0.3.2.tar.gz

NONCONS=0     # Word not constructable from letter set.
CONS=1        # Constructable.
SUCCESS=0
NG=1
FAILURE=''
NULL=0        # Zero out value of letter (if found).
MINWLEN=3     # Minimum word length.
MAXCAT=5      # Maximum number of words in a given category.
PENALTY=200   # General-purpose penalty for unacceptable words.
total=
E_DUP=70      # Duplicate word error.

TIMEOUT=10    # Time for word input.

NVLET=10      # 10 letters for non-vulnerable.
VULET=13      # 13 letters for vulnerable (not yet implemented).

declare -a Words
declare -a Status
declare -a Score=( 0 0 0 0 0 0 0 0 0 0 0 )


letters=( a n s r t m l k p r b c i d s i d z e w u e t f
e y e r e f e g t g h h i t r s c i t i d i j a t a o l a
m n a n o v n w o s e l n o s p a q e e r a b r s a o d s
t g t i t l u e u v n e o x y m r k )
#  Letter distribution table shamelessly borrowed from "Wordy" game,
#+ ca. 1992, written by a certain fine fellow named Mendel Cooper.

declare -a LS

numelements=${#letters[@]}
randseed="$1"

instructions ()
{
  clear
  echo "Welcome to QUACKEY, the anagramming word construction game."; echo
  echo -n "Do you need instructions? (y/n) "; read ans

   if [ "$ans" = "y" -o "$ans" = "Y" ]; then
     clear
     echo -e '\E[31;47m'  # Red foreground. '\E[34;47m' for blue.
     cat <<INSTRUCTION1

QUACKEY is a variant of Perquackey [TM].
The rules are the same, but the scoring is simplified
and plurals of previously played words are allowed.
"Vulnerable" play is not yet implemented,
but it is otherwise feature-complete.

As the game begins, the player gets 10 letters.
The object is to construct valid dictionary words
of at least 3-letter-length from the letterset.
Each word-length category
-- 3-letter, 4-letter, 5-letter, ... --
fills up with the fifth word entered,
and no further words in that category are accepted.

The penalty for too-short (two-letter), duplicate, unconstructable,
and invalid (not in dictionary) words is -200. The same penalty applies
to attempts to enter a word in a filled-up category.

INSTRUCTION1

  echo -n "Hit ENTER for next page of instructions. "; read az1

     cat <<INSTRUCTION2

The scoring mostly corresponds to classic Perquackey:
The first 3-letter word scores    60, plus   10 for each additional one.
The first 4-letter word scores   120, plus   20 for each additional one.
The first 5-letter word scores   200, plus   50 for each additional one.
The first 6-letter word scores   300, plus  100 for each additional one.
The first 7-letter word scores   500, plus  150 for each additional one.
The first 8-letter word scores   750, plus  250 for each additional one.
The first 9-letter word scores  1000, plus  500 for each additional one.
The first 10-letter word scores 2000, plus 2000 for each additional one.

Category completion bonuses are:
3-letter words   100
4-letter words   200
5-letter words   400
6-letter words   800
7-letter words  2000
8-letter words 10000
This is a simplification of the absurdly complicated Perquackey bonus
scoring system.

INSTRUCTION2

  echo -n "Hit ENTER for final page of instructions. "; read az1

     cat <<INSTRUCTION3


Hitting just ENTER for a word entry ends the game.

Individual word entry is timed to a maximum of 10 seconds.
*** Timing out on an entry ends the game. ***
Other than that, the game is untimed.

--------------------------------------------------
Game statistics are automatically saved to a file.
--------------------------------------------------

For competitive ("duplicate") play, a previous letterset
may be duplicated by repeating the script's random seed,
command-line parameter \$1.
For example, "qky 7633" specifies the letterset 
c a d i f r h u s k ...
INSTRUCTION3

  echo; echo -n "Hit ENTER to begin game. "; read az1

       echo -e "\033[0m"    # Turn off red.
     else clear
  fi

  clear

}



seed_random ()
{                         #  Seed random number generator.
  if [ -n "$randseed" ]   #  Can specify random seed.
  then                    #+ for play in competitive mode.
#   RANDOM="$randseed"
    echo "RANDOM seed set to "$randseed""
  else
    randseed="$$"         # Or get random seed from process ID.
    echo "RANDOM seed not specified, set to Process ID of script ($$)."
  fi

  RANDOM="$randseed"

  echo
}


get_letset ()
{
  element=0
  echo -n "Letterset:"

  for lset in $(seq $NVLET)
  do  # Pick random letters to fill out letterset.
    LS[element]="${letters[$((RANDOM%numelements))]}"
    ((element++))
  done

  echo
  echo "${LS[@]}"

}


add_word ()
{
  wrd="$1"
  local idx=0

  Status[0]=""
  Status[3]=""
  Status[4]=""

  while [ "${Words[idx]}" != '' ]
  do
    if [ "${Words[idx]}" = "$wrd" ]
    then
      Status[3]="Duplicate-word-PENALTY"
      let "Score[0]= 0 - $PENALTY"
      let "Score[1]-=$PENALTY"
      return $E_DUP
    fi

    ((idx++))
  done

  Words[idx]="$wrd"
  get_score

}

get_score()
{
  local wlen=0
  local score=0
  local bonus=0
  local first_word=0
  local add_word=0
  local numwords=0

  wlen=${#wrd}
  numwords=${Score[wlen]}
  Score[2]=0
  Status[4]=""   # Initialize "bonus" to 0.

  case "$wlen" in
    3) first_word=60
       add_word=10;;
    4) first_word=120
       add_word=20;;
    5) first_word=200
       add_word=50;;
    6) first_word=300
       add_word=100;;
    7) first_word=500
       add_word=150;;
    8) first_word=750
       add_word=250;;
    9) first_word=1000
       add_word=500;;
   10) first_word=2000
       add_word=2000;;   # This category modified from original rules!
      esac

  ((Score[wlen]++))
  if [ ${Score[wlen]} -eq $MAXCAT ]
  then   # Category completion bonus scoring simplified!
    case $wlen in
      3 ) bonus=100;;
      4 ) bonus=200;;
      5 ) bonus=400;;
      6 ) bonus=800;;
      7 ) bonus=2000;;
      8 ) bonus=10000;;
    esac  # Needn't worry about 9's and 10's.
    Status[4]="Category-$wlen-completion***BONUS***"
    Score[2]=$bonus
  else
    Status[4]=""   # Erase it.
  fi


    let "score =  $first_word +   $add_word * $numwords"
    if [ "$numwords" -eq 0 ]
    then
      Score[0]=$score
    else
      Score[0]=$add_word
    fi   #  All this to distinguish last-word score
         #+ from total running score.
  let "Score[1] += ${Score[0]}"
  let "Score[1] += ${Score[2]}"

}



get_word ()
{
  local wrd=''
  read -t $TIMEOUT wrd   # Timed read.
  echo $wrd
}

is_constructable ()
{ # This was the most complex and difficult-to-write function.
  local -a local_LS=( "${LS[@]}" )  # Local copy of letter set.
  local is_found=0
  local idx=0
  local pos
  local strlen
  local local_word=( "$1" )
  strlen=${#local_word}

  while [ "$idx" -lt "$strlen" ]
  do
    is_found=$(expr index "${local_LS[*]}" "${local_word:idx:1}")
    if [ "$is_found" -eq "$NONCONS" ] # Not constructable!
    then
      echo "$FAILURE"; return
    else
      ((pos = ($is_found - 1) / 2))   # Compensate for spaces betw. letters!
      local_LS[pos]=$NULL             # Zero out used letters.
      ((idx++))                       # Bump index.
    fi
  done

  echo "$SUCCESS"
  return
}

is_valid ()
{ # Surprisingly easy to check if word in dictionary ...
  fgrep -qw "$1" "$WLIST"   # ... thanks to 'grep' ...
  echo $?
}

check_word ()
{
  if [ -z "$1" ]
  then
    return
  fi

  Status[1]=""
  Status[2]=""
  Status[3]=""
  Status[4]=""

  iscons=$(is_constructable "$1")
  if [ "$iscons" ]
  then
    Status[1]="constructable" 
    v=$(is_valid "$1")
    if [ "$v" -eq "$SUCCESS" ]
    then
      Status[2]="valid" 
      strlen=${#1}

      if [ ${Score[strlen]} -eq "$MAXCAT" ]   # Category full!
      then
        Status[3]="Category-$strlen-overflow-PENALTY"
        return $NG
      fi

      case "$strlen" in
        1 | 2 )
        Status[3]="Two-letter-word-PENALTY"
        return $NG;;
        * ) 
	Status[3]=""
	return $SUCCESS;;
      esac
    else
      Status[3]="Not-valid-PENALTY"
      return $NG
    fi
  else
    Status[3]="Not-constructable-PENALTY" 
      return $NG
  fi

  ### FIXME: Streamline the above code.

}


display_words ()
{
  local idx=0
  local wlen0

  clear
  echo "Letterset:   ${LS[@]}"
  echo "Threes:    Fours:    Fives:     Sixes:    Sevens:    Eights:"
  echo "------------------------------------------------------------"


   
  while [ "${Words[idx]}" != '' ]
  do
   wlen0=${#Words[idx]}
   case "$wlen0" in
     3) ;;
     4) echo -n "           " ;;
     5) echo -n "                     " ;;
     6) echo -n "                                " ;;
     7) echo -n "                                          " ;;
     8) echo -n "                                                     " ;;
   esac
   echo "${Words[idx]}"
   ((idx++))
  done

  ### FIXME: The word display is pretty crude.
}


play ()
{
  word="Start game"   # Dummy word, to start ...

  while [ "$word" ]   #  If player just hits return (blank word),
  do                  #+ then game ends.
    echo "$word: "${Status[@]}""
    echo -n "Last score: [${Score[0]}]   TOTAL score: [${Score[1]}]:     Next word: "
    total=${Score[1]}
    word=$(get_word)
    check_word "$word"

    if [ "$?" -eq "$SUCCESS" ]
    then
      add_word "$word"
    else
      let "Score[0]= 0 - $PENALTY"
      let "Score[1]-=$PENALTY"
    fi

  display_words
  done   # Exit game.

  ### FIXME: The play () function calls too many other functions.
  ### This is perilously close to "spaghetti code" ...
}

end_of_game ()
{ # Save and display stats.

  #######################Autosave##########################
  savefile=qky.save.$$
  #                 ^^ PID of script
  echo `date` >> $savefile
  echo "Letterset # $randseed  (random seed) ">> $savefile
  echo -n "Letterset: " >> $savefile
  echo "${LS[@]}" >> $savefile
  echo "---------" >> $savefile
  echo "Words constructed:" >> $savefile
  echo "${Words[@]}" >> $savefile
  echo >> $savefile
  echo "Score: $total" >> $savefile

  echo "Statistics for this round saved in \""$savefile"\""
  #########################################################

  echo "Score for this round: $total"
  echo "Words:  ${Words[@]}"
}

# ---------#
instructions
seed_random
get_letset
play
end_of_game
# ---------#

exit $?

# TODO:
#
# 1) Clean up code!
# 2) Prettify the display_words () function (maybe with widgets?).
# 3) Improve the time-out ... maybe change to untimed entry,
#+   but with a time limit for the overall round.   
# 4) An on-screen countdown timer would be nice.
# 5) Implement "vulnerable" mode of play.
# 6) Improve save-to-file capability (and maybe make it optional).
# 7) Fix bugs!!!

# Reference for more info:
# http://bash.neuralshortcircuit.com/qky.README.html

Example A-44. Nim

#!/bin/bash
# nim.sh: Game of Nim

# Author: Mendel Cooper
# Reldate: 15 July 2008
# License: GPL3

ROWS=5     # Five rows of pegs (or matchsticks).
WON=91     # Exit codes to keep track of wins/losses.
LOST=92    # Possibly useful if running in batch mode.  
QUIT=99
peg_msg=   # Peg/Pegs?
Rows=( 0 5 4 3 2 1 )   # Array holding play info.
# ${Rows[0]} holds total number of pegs, updated after each turn.
# Other array elements hold number of pegs in corresponding row.

instructions ()
{
  clear
  tput bold
  echo "Welcome to the game of Nim."; echo
  echo -n "Do you need instructions? (y/n) "; read ans

   if [ "$ans" = "y" -o "$ans" = "Y" ]; then
     clear
     echo -e '\E[33;41m'  # Yellow fg., over red bg.; bold.
     cat <<INSTRUCTIONS

Nim is a game with roots in the distant past.
This particular variant starts with five rows of pegs.

1:    | | | | | 
2:     | | | | 
3:      | | | 
4:       | | 
5:        | 

The number at the left identifies the row.

The human player moves first, and alternates turns with the bot.
A turn consists of removing at least one peg from a single row.
It is permissable to remove ALL the pegs from a row.
For example, in row 2, above, the player can remove 1, 2, 3, or 4 pegs.
The player who removes the last peg loses.

The strategy consists of trying to be the one who removes
the next-to-last peg(s), leaving the loser with the final peg.

To exit the game early, hit ENTER during your turn.
INSTRUCTIONS

echo; echo -n "Hit ENTER to begin game. "; read azx

      echo -e "\033[0m"    # Restore display.
      else tput sgr0; clear
  fi

clear

}


tally_up ()
{
  let "Rows[0] = ${Rows[1]} + ${Rows[2]} + ${Rows[3]} + ${Rows[4]} + \
  ${Rows[5]}"    # Add up how many pegs remaining.
}


display ()
{
  index=1   # Start with top row.
  echo

  while [ "$index" -le "$ROWS" ]
  do
    p=${Rows[index]}
    echo -n "$index:   "          # Show row number.

  # ------------------------------------------------
  # Two concurrent inner loops.

      indent=$index
      while [ "$indent" -gt 0 ]
      do
        echo -n " "               # Staggered rows.
        ((indent--))              # Spacing between pegs.
      done

    while [ "$p" -gt 0 ]
    do
      echo -n "| "
      ((p--))
    done
  # -----------------------------------------------

  echo
  ((index++))
  done  

  tally_up

  rp=${Rows[0]}

  if [ "$rp" -eq 1 ]
  then
    peg_msg=peg
    final_msg="Game over."
  else             # Game not yet over . . .
    peg_msg=pegs
    final_msg=""   # . . . So "final message" is blank.
  fi

  echo "      $rp $peg_msg remaining."
  echo "      "$final_msg""


  echo
}

player_move ()
{

  echo "Your move:"

  echo -n "Which row? "
  while read idx
  do                   # Validity check, etc.

    if [ -z "$idx" ]   # Hitting return quits.
    then
        echo "Premature exit."; echo
        tput sgr0      # Restore display.
        exit $QUIT
    fi

    if [ "$idx" -gt "$ROWS" -o "$idx" -lt 1 ]   # Bounds check.
    then
      echo "Invalid row number!"
      echo -n "Which row? "
    else
      break
    fi
    # TODO:
    # Add check for non-numeric input.
    # Also, script crashes on input outside of range of long double.
    # Fix this.

  done

  echo -n "Remove how many? "
  while read num
  do                   # Validity check.

  if [ -z "$num" ]
  then
    echo "Premature exit."; echo
    tput sgr0          # Restore display.
    exit $QUIT
  fi

    if [ "$num" -gt ${Rows[idx]} -o "$num" -lt 1 ]
    then
      echo "Cannot remove $num!"
      echo -n "Remove how many? "
    else
      break
    fi
  done
  # TODO:
  # Add check for non-numeric input.
  # Also, script crashes on input outside of range of long double.
  # Fix this.

  let "Rows[idx] -= $num"

  display
  tally_up

  if [ ${Rows[0]} -eq 1 ]
  then
   echo "      Human wins!"
   echo "      Congratulations!"
   tput sgr0   # Restore display.
   echo
   exit $WON
  fi

  if [ ${Rows[0]} -eq 0 ]
  then          # Snatching defeat from the jaws of victory . . .
    echo "      Fool!"
    echo "      You just removed the last peg!"
    echo "      Bot wins!"
    tput sgr0   # Restore display.
    echo
    exit $LOST
  fi
}


bot_move ()
{

  row_b=0
  while [[ $row_b -eq 0 || ${Rows[row_b]} -eq 0 ]]
  do
    row_b=$RANDOM          # Choose random row.
    let "row_b %= $ROWS"
  done


  num_b=0
  r0=${Rows[row_b]}

  if [ "$r0" -eq 1 ]
  then
    num_b=1
  else
    let "num_b = $r0 - 1"
         #  Leave only a single peg in the row.
  fi     #  Not a very strong strategy,
         #+ but probably a bit better than totally random.

  let "Rows[row_b] -= $num_b"
  echo -n "Bot:  "
  echo "Removing from row $row_b ... "

  if [ "$num_b" -eq 1 ]
  then
    peg_msg=peg
  else
    peg_msg=pegs
  fi

  echo "      $num_b $peg_msg."

  display
  tally_up

  if [ ${Rows[0]} -eq 1 ]
  then
   echo "      Bot wins!"
   tput sgr0   # Restore display.
   exit $WON
  fi

}


# ================================================== #
instructions     # If human player needs them . . .
tput bold        # Bold characters for easier viewing.
display          # Show game board.

while [ true ]   # Main loop.
do               # Alternate human and bot turns.
  player_move
  bot_move
done
# ================================================== #

# Exercise:
# --------
# Improve the bot's strategy.
# There is, in fact, a Nim strategy that can force a win.
# See the Wikipedia article on Nim:  http://en.wikipedia.org/wiki/Nim
# Recode the bot to use this strategy (rather difficult).

#  Curiosities:
#  -----------
#  Nim played a prominent role in Alain Resnais' 1961 New Wave film,
#+ Last Year at Marienbad.
#
#  In 1978, Leo Christopherson wrote an animated version of Nim,
#+ Android Nim, for the TRS-80 Model I.

Example A-45. A command-line stopwatch

#!/bin/sh
# sw.sh
# A command-line Stopwatch

# Author: PАdraig Brady
#    http://www.pixelbeat.org/scripts/sw
#    (Minor reformatting by ABS Guide author.)
#    Used in ABS Guide with script author's permission.
# Notes:
#    This script starts a few processes per lap, in addition to
#    the shell loop processing, so the assumption is made that
#    this takes an insignificant amount of time compared to
#    the response time of humans (~.1s) (or the keyboard
#    interrupt rate (~.05s)).
#    '?' for splits must be entered twice if characters
#    (erroneously) entered before it (on the same line).
#    '?' since not generating a signal may be slightly delayed
#    on heavily loaded systems.
#    Lap timings on ubuntu may be slightly delayed due to:
#    https://bugs.launchpad.net/bugs/62511
# Changes:
#    V1.0, 23 Aug 2005, Initial release
#    V1.1, 26 Jul 2007, Allow both splits and laps from single invocation.
#                       Only start timer after a key is pressed.
#                       Indicate lap number
#                       Cache programs at startup so there is less error
#                       due to startup delays.
#    V1.2, 01 Aug 2007, Work around `date` commands that don't have
#                       nanoseconds.
#                       Use stty to change interrupt keys to space for
#                       laps etc.
#                       Ignore other input as it causes problems.
#    V1.3, 01 Aug 2007, Testing release.
#    V1.4, 02 Aug 2007, Various tweaks to get working under ubuntu
#                       and Mac OS X.
#    V1.5, 27 Jun 2008, set LANG=C as got vague bug report about it.

export LANG=C

ulimit -c 0   # No coredumps from SIGQUIT.
trap '' TSTP  # Ignore Ctrl-Z just in case.
save_tty=`stty -g` && trap "stty $save_tty" EXIT  # Restore tty on exit.
stty quit ' ' # Space for laps rather than Ctrl-\.
stty eof  '?' # ? for splits rather than Ctrl-D.
stty -echo    # Don't echo input.

cache_progs() {
    stty > /dev/null
    date > /dev/null
    grep . < /dev/null
    (echo "import time" | python) 2> /dev/null
    bc < /dev/null
    sed '' < /dev/null
    printf '1' > /dev/null
    /usr/bin/time false 2> /dev/null
    cat < /dev/null
}
cache_progs   # To minimise startup delay.

date +%s.%N | grep -qF 'N' && use_python=1 # If `date` lacks nanoseconds.
now() {
    if [ "$use_python" ]; then
        echo "import time; print time.time()" 2>/dev/null | python
    else
        printf "%.2f" `date +%s.%N`
    fi
}

fmt_seconds() {
    seconds=$1
    mins=`echo $seconds/60 | bc`
    if [ "$mins" != "0" ]; then
        seconds=`echo "$seconds - ($mins*60)" | bc`
        echo "$mins:$seconds"
    else
        echo "$seconds"
    fi
}

total() {
    end=`now`
    total=`echo "$end - $start" | bc`
    fmt_seconds $total
}

stop() {
    [ "$lapped" ] && lap "$laptime" "display"
    total
    exit
}

lap() {
    laptime=`echo "$1" | sed -n 's/.*real[^0-9.]*\(.*\)/\1/p'`
    [ ! "$laptime" -o "$laptime" = "0.00" ] && return
    # Signals too frequent.
    laptotal=`echo $laptime+0$laptotal | bc`
    if [ "$2" = "display" ]; then
        lapcount=`echo 0$lapcount+1 | bc`
        laptime=`fmt_seconds $laptotal`
        echo $laptime "($lapcount)"
        lapped="true"
        laptotal="0"
    fi
}

echo -n "Space for lap | ? for split | Ctrl-C to stop | Space to start...">&2

while true; do
    trap true INT QUIT  # Set signal handlers.
    laptime=`/usr/bin/time -p 2>&1 cat >/dev/null`
    ret=$?
    trap '' INT QUIT    # Ignore signals within this script.
    if [ $ret -eq 1 -o $ret -eq 2 -o $ret -eq 130 ]; then # SIGINT = stop
        [ ! "$start" ] && { echo >&2; exit; }
        stop
    elif [ $ret -eq 3 -o $ret -eq 131 ]; then             # SIGQUIT = lap
        if [ ! "$start" ]; then
            start=`now` || exit 1
            echo >&2
            continue
        fi
        lap "$laptime" "display"
    else                # eof = split
        [ ! "$start" ] && continue
        total
        lap "$laptime"  # Update laptotal.
    fi
done

exit $?

Example A-46. An all-purpose shell scripting homework assignment solution

#!/bin/bash
#  homework.sh: All-purpose homework assignment solution.
#  Author: M. Leo Cooper
#  If you substitute your own name as author, then it is plagiarism,
#+ possibly a lesser sin than cheating on your homework!
#  License: Public Domain

#  This script may be turned in to your instructor
#+ in fulfillment of ALL shell scripting homework assignments.
#  It's sparsely commented, but you, the student, can easily remedy that.
#  The script author repudiates all responsibility!

DLA=1
P1=2
P2=4
P3=7
PP1=0
PP2=8
MAXL=9
E_LZY=99

declare -a L
L[0]="3 4 0 17 29 8 13 18 19 17 20 2 19 14 17 28"
L[1]="8 29 12 14 18 19 29 4 12 15 7 0 19 8 2 0 11 11 24 29 17 4 6 17 4 19"
L[2]="29 19 7 0 19 29 8 29 7 0 21 4 29 13 4 6 11 4 2 19 4 3"
L[3]="19 14 29 2 14 12 15 11 4 19 4 29 19 7 8 18 29"
L[4]="18 2 7 14 14 11 22 14 17 10 29 0 18 18 8 6 13 12 4 13 19 26"
L[5]="15 11 4 0 18 4 29 0 2 2 4 15 19 29 12 24 29 7 20 12 1 11 4 29"
L[6]="4 23 2 20 18 4 29 14 5 29 4 6 17 4 6 8 14 20 18 29"
L[7]="11 0 25 8 13 4 18 18 27"
L[8]="0 13 3 29 6 17 0 3 4 29 12 4 29 0 2 2 14 17 3 8 13 6 11 24 26"
L[9]="19 7 0 13 10 29 24 14 20 26"

declare -a \
alph=( A B C D E F G H I J K L M N O P Q R S T U V W X Y Z . , : ' ' )


pt_lt ()
{
  echo -n "${alph[$1]}"
  echo -n -e "\a"
  sleep $DLA
}

b_r ()
{
 echo -e '\E[31;48m\033[1m'
}

cr ()
{
 echo -e "\a"
 sleep $DLA
}

restore ()
{
  echo -e '\033[0m'            # Bold off.
  tput sgr0                    # Normal.
}


p_l ()
{
  for ltr in $1
  do
    pt_lt "$ltr"
  done
}

# ----------------------
b_r

for i in $(seq 0 $MAXL)
do
  p_l "${L[i]}"
  if [[ "$i" -eq "$P1" || "$i" -eq "$P2" || "$i" -eq "$P3" ]]
  then
    cr
  elif [[ "$i" -eq "$PP1" || "$i" -eq "$PP2" ]]
  then
    cr; cr
  fi
done

restore
# ----------------------

echo

exit $E_LZY

#  A typical example of an obfuscated script that is difficult
#+ to understand, and frustrating to maintain.
#  In your career as a sysadmin, you'll run into these critters
#+ all too often.

Example A-47. The Knight's Tour

#!/bin/bash
# ktour.sh

# author: mendel cooper
# reldate: 12 Jan 2009
# license: public domain
# (Not much sense in GPLing something that's pretty much in the common
#+ domain anyhow.)

###################################################################
#             The Knight's Tour, a classic problem.               #
#             =====================================               #
#  The knight must move onto every square of the chess board,     #
#  but cannot revisit any square he has already visited.          #
#                                                                 #
#  And just why is Sir Knight unwelcome for a return visit?       #
#  Could it be that he has a habit of partying into the wee hours #
#+ of the morning?                                                #
#  Possibly he leaves pizza crusts in the bed, empty beer bottles #
#+ all over the floor, and clogs the plumbing. ...                #
#                                                                 #
#  -------------------------------------------------------------  #
#                                                                 #
#  Usage: ktour.sh [start-square] [stupid]                        #
#                                                                 #
#  Note that start-square can be a square number                  #
#+ in the range 0 - 63 ... or                                     #
#  a square designator in conventional chess notation,            #
#  such as a1, f5, h3, etc.                                       #
#                                                                 #
#  If start-square-number not supplied,                           #
#+ then starts on a random square somewhere on the board.         #
#                                                                 #
# "stupid" as second parameter sets the stupid strategy.          #
#                                                                 #
#  Examples:                                                      #
#  ktour.sh 23          starts on square #23 (h3)                 #
#  ktour.sh g6 stupid   starts on square #46,                     #
#                       using "stupid" (non-Warnsdorff) strategy. #
###################################################################

DEBUG=      # Set this to echo debugging info to stdout.
SUCCESS=0
FAIL=99
BADMOVE=-999
FAILURE=1
LINELEN=21  # How many moves to display per line.
# ---------------------------------------- #
# Board array params
ROWS=8   # 8 x 8 board.
COLS=8
let "SQUARES = $ROWS * $COLS"
let "MAX = $SQUARES - 1"
MIN=0
# 64 squares on board, indexed from 0 to 63.

VISITED=1
UNVISITED=-1
UNVSYM="##"
# ---------------------------------------- #
# Global variables.
startpos=    # Starting position (square #, 0 - 63).
currpos=     # Current position.
movenum=     # Move number.
CRITPOS=37   # Have to patch for f5 starting position!

declare -i board
# Use a one-dimensional array to simulate a two-dimensional one.
# This can make life difficult and result in ugly kludges; see below.
declare -i moves  # Offsets from current knight position.


initialize_board ()
{
  local idx

  for idx in {0..63}
  do
    board[$idx]=$UNVISITED
  done
}



print_board ()
{
  local idx

  echo "    _____________________________________"
  for row in {7..0}               #  Reverse order of rows ...
  do                              #+ so it prints in chessboard order.
    let "rownum = $row + 1"       #  Start numbering rows at 1.
    echo -n "$rownum  |"          #  Mark board edge with border and
    for column in {0..7}          #+ "algebraic notation."
    do
      let "idx = $ROWS*$row + $column"
      if [ ${board[idx]} -eq $UNVISITED ]
      then
        echo -n "$UNVSYM   "      ##
      else                        # Mark square with move number.
        printf "%02d " "${board[idx]}"; echo -n "  "
      fi
    done
    echo -e -n "\b\b\b|"  # \b is a backspace.
    echo                  # -e enables echoing escaped chars.
  done

  echo "    -------------------------------------"
  echo "     a    b    c    d    e    f    g    h"
}



failure()
{ # Whine, then bail out.
  echo
  print_board
  echo
  echo    "   Waah!!! Ran out of squares to move to!"
  echo -n "   Knight's Tour attempt ended"
  echo    " on $(to_algebraic $currpos) [square #$currpos]"
  echo    "   after just $movenum moves!"
  echo
  exit $FAIL
}



xlat_coords ()   #  Translate x/y coordinates to board position
{                #+ (board-array element #).
  #  For user input of starting board position as x/y coords.
  #  This function not used in initial release of ktour.sh.
  #  May be used in an updated version, for compatibility with
  #+ standard implementation of the Knight's Tour in C, Python, etc.
  if [ -z "$1" -o -z "$2" ]
  then
    return $FAIL
  fi

  local xc=$1
  local yc=$2

  let "board_index = $xc * $ROWS + yc"

  if [ $board_index -lt $MIN -o $board_index -gt $MAX ]
  then
    return $FAIL    # Strayed off the board!
  else
    return $board_index
  fi
}



to_algebraic ()   #  Translate board position (board-array element #)
{                 #+ to standard algebraic notation used by chess players.
  if [ -z "$1" ]
  then
    return $FAIL
  fi

  local element_no=$1   # Numerical board position.
  local col_arr=( a b c d e f g h )
  local row_arr=( 1 2 3 4 5 6 7 8 )

  let "row_no = $element_no / $ROWS"
  let "col_no = $element_no % $ROWS"
  t1=${col_arr[col_no]}; t2=${row_arr[row_no]}
  local apos=$t1$t2   # Concatenate.
  echo $apos
}



from_algebraic ()   #  Translate standard algebraic chess notation
{                   #+ to numerical board position (board-array element #).
                    #  Or recognize numerical input & return it unchanged.
  if [ -z "$1" ]
  then
    return $FAIL
  fi   # If no command-line arg, then will default to random start pos.

  local ix
  local ix_count=0
  local b_index     # Board index [0-63]
  local alpos="$1"

  arow=${alpos:0:1} # position = 0, length = 1
  acol=${alpos:1:1}

  if [[ $arow =~ [[:digit:]] ]]   #  Numerical input?
  then       #  POSIX char class
    if [[ $acol =~ [[:alpha:]] ]] # Number followed by a letter? Illegal!
      then return $FAIL
    else if [ $alpos -gt $MAX ]   # Off board?
      then return $FAIL
    else return $alpos            #  Return digit(s) unchanged . . .
      fi                          #+ if within range.
    fi
  fi

  if [[ $acol -eq $MIN || $acol -gt $ROWS ]]
  then        # Outside of range 1 - 8?
    return $FAIL
  fi

  for ix in a b c d e f g h
  do  # Convert column letter to column number.
   if [ "$arow" = "$ix" ]
   then
     break
   fi
  ((ix_count++))    # Find index count.
  done

  ((acol--))        # Decrementing converts to zero-based array.
  let "b_index = $ix_count + $acol * $ROWS"

  if [ $b_index -gt $MAX ]   # Off board?
  then
    return $FAIL
  fi
    
  return $b_index

}


generate_moves ()   #  Calculate all valid knight moves,
{                   #+ relative to current position ($1),
                    #+ and store in ${moves} array.
  local kt_hop=1    #  One square  :: short leg of knight move.
  local kt_skip=2   #  Two squares :: long leg  of knight move.
  local valmov=0    #  Valid moves.
  local row_pos; let "row_pos = $1 % $COLS"


  let "move1 = -$kt_skip + $ROWS"           # 2 sideways to-the-left,  1 up
    if [[ `expr $row_pos - $kt_skip` -lt $MIN ]]   # An ugly, ugly kludge!
    then                                           # Can't move off board.
      move1=$BADMOVE                               # Not even temporarily.
    else
      ((valmov++))
    fi
  let "move2 = -$kt_hop + $kt_skip * $ROWS" # 1 sideways to-the-left,  2 up
    if [[ `expr $row_pos - $kt_hop` -lt $MIN ]]    # Kludge continued ...
    then
      move2=$BADMOVE
    else
      ((valmov++))
    fi
  let "move3 =  $kt_hop + $kt_skip * $ROWS" # 1 sideways to-the-right, 2 up
    if [[ `expr $row_pos + $kt_hop` -ge $COLS ]]
    then
      move3=$BADMOVE
    else
      ((valmov++))
    fi
  let "move4 =  $kt_skip + $ROWS"           # 2 sideways to-the-right, 1 up
    if [[ `expr $row_pos + $kt_skip` -ge $COLS ]]
    then
      move4=$BADMOVE
    else
      ((valmov++))
    fi
  let "move5 =  $kt_skip - $ROWS"           # 2 sideways to-the-right, 1 dn
    if [[ `expr $row_pos + $kt_skip` -ge $COLS ]]
    then
      move5=$BADMOVE
    else
      ((valmov++))
    fi
  let "move6 =  $kt_hop - $kt_skip * $ROWS" # 1 sideways to-the-right, 2 dn
    if [[ `expr $row_pos + $kt_hop` -ge $COLS ]]
    then
      move6=$BADMOVE
    else
      ((valmov++))
    fi
  let "move7 = -$kt_hop - $kt_skip * $ROWS" # 1 sideways to-the-left,  2 dn
    if [[ `expr $row_pos - $kt_hop` -lt $MIN ]]
    then
      move7=$BADMOVE
    else
      ((valmov++))
    fi
  let "move8 = -$kt_skip - $ROWS"           # 2 sideways to-the-left,  1 dn
    if [[ `expr $row_pos - $kt_skip` -lt $MIN ]]
    then
      move8=$BADMOVE
    else
      ((valmov++))
    fi   # There must be a better way to do this.

  local m=( $valmov $move1 $move2 $move3 $move4 $move5 $move6 $move7 $move8 )
  # ${moves[0]} = number of valid moves.
  # ${moves[1]} ... ${moves[8]} = possible moves.
  echo "${m[*]}"    # Elements of array to stdout for capture in a var.

}



is_on_board ()  # Is position actually on the board?
{
  if [[ "$1" -lt "$MIN" || "$1" -gt "$MAX" ]]
  then
    return $FAILURE
  else
    return $SUCCESS
  fi
}



do_move ()      # Move the knight!
{
  local valid_moves=0
  local aapos
  currposl="$1"
  lmin=$ROWS
  iex=0
  squarel=
  mpm=
  mov=
  declare -a p_moves

  ########################## DECIDE-MOVE #############################
  if [ $startpos -ne $CRITPOS ]
  then   # CRITPOS = square #37
    decide_move
  else                     # Needs a special patch for startpos=37 !!!
    decide_move_patched    # Why this particular move and no other ???
  fi
  ####################################################################

  (( ++movenum ))          # Increment move count.
  let "square = $currposl + ${moves[iex]}"

  ##################    DEBUG    ###############
  if [ "$DEBUG" ]
    then debug   # Echo debugging information.
  fi
  ##############################################

  if [[ "$square" -gt $MAX || "$square" -lt $MIN ||
        ${board[square]} -ne $UNVISITED ]]
  then
    (( --movenum ))              #  Decrement move count,
    echo "RAN OUT OF SQUARES!!!" #+ since previous one was invalid.
    return $FAIL
  fi

  board[square]=$movenum
  currpos=$square       # Update current position.
  ((valid_moves++));    # moves[0]=$valid_moves
  aapos=$(to_algebraic $square)
  echo -n "$aapos "
  test $(( $Moves % $LINELEN )) -eq 0 && echo
  # Print LINELEN=21 moves per line. A valid tour shows 3 complete lines.
  return $valid_moves   # Found a square to move to!
}



do_move_stupid()   #  Dingbat algorithm,
{                  #+ courtesy of script author, *not* Warnsdorff.
  local valid_moves=0
  local movloc
  local squareloc
  local aapos
  local cposloc="$1"

  for movloc in {1..8}
  do       # Move to first-found unvisited square.
    let "squareloc = $cposloc + ${moves[movloc]}"
    is_on_board $squareloc
    if [ $? -eq $SUCCESS ] && [ ${board[squareloc]} -eq $UNVISITED ]
    then   # Add conditions to above if-test to improve algorithm.
      (( ++movenum ))
      board[squareloc]=$movenum
      currpos=$squareloc     # Update current position.
      ((valid_moves++));     # moves[0]=$valid_moves
      aapos=$(to_algebraic $squareloc)
      echo -n "$aapos "
      test $(( $Moves % $LINELEN )) -eq 0 && echo   # Print 21 moves/line.
      return $valid_moves    # Found a square to move to!
    fi
  done

  return $FAIL
  #  If no square found in all 8 loop iterations,
  #+ then Knight's Tour attempt ends in failure.

  #  Dingbat algorithm will typically fail after about 30 - 40 moves,
  #+ but executes _much_ faster than Warnsdorff's in do_move() function.
}



decide_move ()         #  Which move will we make?
{                      #  But, fails on startpos=37 !!!
  for mov in {1..8}
  do
    let "squarel = $currposl + ${moves[mov]}"
    is_on_board $squarel
    if [[ $? -eq $SUCCESS && ${board[squarel]} -eq $UNVISITED ]]
    then   #  Find accessible square with least possible future moves.
           #  This is Warnsdorff's algorithm.
           #  What happens is that the knight wanders toward the outer edge
           #+ of the board, then pretty much spirals inward.
           #  Given two or more possible moves with same value of
           #+ least-possible-future-moves, this implementation chooses
           #+ the _first_ of those moves.
           #  This means that there is not necessarily a unique solution
           #+ for any given starting position.

      possible_moves $squarel
      mpm=$?
      p_moves[mov]=$mpm
      
      if [ $mpm -lt $lmin ]  # If less than previous minimum ...
      then #     ^^
        lmin=$mpm            # Update minimum.
        iex=$mov             # Save index.
      fi

    fi
  done
}



decide_move_patched ()         #  Decide which move to make,
{  #        ^^^^^^^            #+ but only if startpos=37 !!!
  for mov in {1..8}
  do
    let "squarel = $currposl + ${moves[mov]}"
    is_on_board $squarel
    if [[ $? -eq $SUCCESS && ${board[squarel]} -eq $UNVISITED ]]
    then
      possible_moves $squarel
      mpm=$?
      p_moves[mov]=$mpm
      
      if [ $mpm -le $lmin ]  # If less-than-or equal to prev. minimum!
      then #     ^^
        lmin=$mpm
        iex=$mov
      fi

    fi
  done                       # There has to be a better way to do this.
}



possible_moves ()            #  Calculate number of possible moves,
{                            #+ given the current position.

  if [ -z "$1" ]
  then
    return $FAIL
  fi

  local curr_pos=$1
  local valid_movl=0
  local icx=0
  local movl
  local sq
  declare -a movesloc

  movesloc=( $(generate_moves $curr_pos) )

  for movl in {1..8}
  do
    let "sq = $curr_pos + ${movesloc[movl]}"
    is_on_board $sq
    if [ $? -eq $SUCCESS ] && [ ${board[sq]} -eq $UNVISITED ]
    then
      ((valid_movl++));
    fi
  done

  return $valid_movl         # Found a square to move to!
}


strategy ()
{
  echo

  if [ -n "$STUPID" ]
  then
    for Moves in {1..63}
    do
      cposl=$1
      moves=( $(generate_moves $currpos) )
      do_move_stupid "$currpos"
      if [ $? -eq $FAIL ]
      then
        failure
      fi
      done
  fi

  #  Don't need an "else" clause here,
  #+ because Stupid Strategy will always fail and exit!
  for Moves in {1..63}
  do
    cposl=$1
    moves=( $(generate_moves $currpos) )
    do_move "$currpos"
    if [ $? -eq $FAIL ]
    then
      failure
    fi

  done
        #  Could have condensed above two do-loops into a single one,
  echo  #+ but this would have slowed execution.

  print_board
  echo
  echo "Knight's Tour ends on $(to_algebraic $currpos) [square #$currpos]."
  return $SUCCESS
}

debug ()
{       # Enable this by setting DEBUG=1 near beginning of script.
  local n

  echo "================================="
  echo "  At move number  $movenum:"
  echo " *** possible moves = $mpm ***"
# echo "### square = $square ###"
  echo "lmin = $lmin"
  echo "${moves[@]}"

  for n in {1..8}
  do
    echo -n "($n):${p_moves[n]} "
  done

  echo
  echo "iex = $iex :: moves[iex] = ${moves[iex]}"
  echo "square = $square"
  echo "================================="
  echo
} # Gives pretty complete status after ea. move.



# =============================================================== #
# int main () {
from_algebraic "$1"
startpos=$?
if [ "$startpos" -eq "$FAIL" ]          # Okay even if no $1.
then   #         ^^^^^^^^^^^              Okay even if input -lt 0.
  echo "No starting square specified (or illegal input)."
  let "startpos = $RANDOM % $SQUARES"   # 0 - 63 permissable range.
fi


if [ "$2" = "stupid" ]
then
  STUPID=1
  echo -n "     ### Stupid Strategy ###"
else
  STUPID=''
  echo -n "  *** Warnsdorff's Algorithm ***"
fi


initialize_board

movenum=0
board[startpos]=$movenum   # Mark each board square with move number.
currpos=$startpos
algpos=$(to_algebraic $startpos)

echo; echo "Starting from $algpos [square #$startpos] ..."; echo
echo -n "Moves:"

strategy "$currpos"

echo

exit 0   # return 0;

# }      # End of main() pseudo-function.
# =============================================================== #


# Exercises:
# ---------
#
# 1) Extend this example to a 10 x 10 board or larger.
# 2) Improve the "stupid strategy" by modifying the
#    do_move_stupid function.
#    Hint: Prevent straying into corner squares in early moves
#          (the exact opposite of Warnsdorff's algorithm!).
# 3) This script could stand considerable improvement and
#    streamlining, especially in the poorly-written
#    generate_moves() function
#    and in the DECIDE-MOVE patch in the do_move() function.
#    Must figure out why standard algorithm fails for startpos=37 ...
#+   but _not_ on any other, including symmetrical startpos=26.
#    Possibly, when calculating possible moves, counts the move back
#+   to the originating square. If so, it might be a relatively easy fix.

Example A-48. Magic Squares

#!/bin/bash
# msquare.sh
# Magic Square generator (odd-order squares only!)

# Author: mendel cooper
# reldate: 19 Jan. 2009
# License: Public Domain
# A C-program by Kwon Young Shin inspired this script.
# See http://user.chollian.net/~brainstm/MagicSquare.htm ...

# Definition: A "magic square" is a two-dimensional array
#             of integers in which all the rows, columns,
#             and *long* diagonals add up to the same number.
#             Being "square," the array has the same number
#             of rows and columns.
# An example of a magic square of order 3 is:
#   8  1  6   
#   3  5  7   
#   4  9  2   
# All the rows, columns, and long diagonals add up to 15.


# Globals
EVEN=2
MAXSIZE=31   # 31 rows x 31 cols.
E_usage=90   # Invocation error.
dimension=
declare -i square

usage_message ()
{
  echo "Usage: $0 square-size"
  echo "   ... where \"square-size\" is an ODD integer"
  echo "       in the range 3 - 31."
  #  Actually works for squares up to order 159,
  #+ but large squares will not display pretty-printed in a term window.
  #  Try increasing MAXSIZE, above.
  exit $E_usage
}


calculate ()       # Here's where the actual work gets done.
{
  local row col index dimadj j k cell_val=1
  dimension=$1

  let "dimadj = $dimension * 3"; let "dimadj /= 2"   # x 1.5, then truncate.

  for ((j=0; j < dimension; j++))
  do
    for ((k=0; k < dimension; k++))
    do  # Calculate indices, then convert to 1-dim. array index.
        # Bash doesn't support multidimensional arrays. Pity.
      let "col = $k - $j + $dimadj"; let "col %= $dimension"
      let "row = $j * 2 - $k + $dimension"; let "row %= $dimension"
      let "index = $row*($dimension) + $col"
      square[$index]=cell_val; ((cell_val++))
    done
  done
}     # Plain math, no visualization required.


print_square ()               # Output square, one row at a time.
{
  local row col idx d1
  let "d1 = $dimension - 1"   # Adjust for zero-indexed array.
 
  for row in $(seq 0 $d1)
  do

    for col in $(seq 0 $d1)
    do
      let "idx = $row * $dimension + $col"
      printf "%3d " "${square[idx]}"; echo -n "  "
    done   # Displays up to 13-order neatly in 80-column term window.

    echo   # Newline after each row.
  done
}


#################################################
if [[ -z "$1" ]] || [[ "$1" -gt $MAXSIZE ]]
then
  usage_message
fi

let "test_even = $1 % $EVEN"
if [ $test_even -eq 0 ]
then           # Can't handle even-order squares.
  usage_message
fi

calculate $1
print_square   # echo "${square[@]}"   # DEBUG

exit $?
#################################################


# Exercises:
# ---------
# 1) Add a function to calculate the sum of each row, column,
#    and *long* diagonal. The sums must match.
#    This is the "magic constant" of that particular order square.
# 2) Have the print_square function auto-calculate how much space
#    to allot between square elements for optimized display.
#    This might require parameterizing the "printf" line.
# 3) Add appropriate functions for generating magic squares
#    with an *even* number of rows/columns.
#    This is non-trivial(!).
#    See the URL for Kwon Young Shin, above, for help.

Example A-49. An alternate version of the getopt-simple.sh script

#!/bin/bash
# UseGetOpt.sh

# Author: Peggy Russell <prusselltechgroup@gmail.com>

UseGetOpt () {
  declare inputOptions
  declare -r E_OPTERR=85
  declare -r ScriptName=${0##*/}
  declare -r ShortOpts="adf:hlt"
  declare -r LongOpts="aoption,debug,file:,help,log,test"

DoSomething () {
    echo "The function name is '${FUNCNAME}'"
    #  Recall that $FUNCNAME is an internal variable
    #+ holding the name of the function it is in.
  }

  inputOptions=$(getopt -o "${ShortOpts}" --long \
              "${LongOpts}" --name "${ScriptName}" -- "${@}")

  if [[ ($? -ne 0) || ($# -eq 0) ]]; then
    echo "Usage: ${ScriptName} [-dhlt] {OPTION...}"
    exit $E_OPTERR
  fi

  eval set -- "${inputOptions}"

  # Only for educational purposes. Can be removed.
  #-----------------------------------------------
  echo "++ Test: Number of arguments: [$#]"
  echo '++ Test: Looping through "$@"'
  for a in "$@"; do
    echo "  ++ [$a]"
  done
  #-----------------------------------------------

  while true; do
    case "${1}" in
      --aoption | -a)  # Argument found.
        echo "Option [$1]"
        ;;

      --debug | -d)    # Enable informational messages.
        echo "Option [$1] Debugging enabled"
        ;;

      --file | -f)     #  Check for optional argument.
        case "$2" in   #+ Double colon is optional argument.
          "")          #  Not there.
              echo "Option [$1] Use default"
              shift
              ;;

          *) # Got it
             echo "Option [$1] Using input [$2]"
             shift
             ;;

        esac
        DoSomething
        ;;

      --log | -l) # Enable Logging.
        echo "Option [$1] Logging enabled"
        ;;

      --test | -t) # Enable testing.
        echo "Option [$1] Testing enabled"
        ;;

      --help | -h)
        echo "Option [$1] Display help"
        break
        ;;

      --)   # Done! $# is argument number for "--", $@ is "--"
        echo "Option [$1] Dash Dash"
        break
        ;;

       *)
        echo "Major internal error!"
        exit 8
        ;;

    esac
    echo "Number of arguments: [$#]"
    shift
  done

  shift
  # Only for educational purposes. Can be removed.
  #----------------------------------------------------------------------
  echo "++ Test: Number of arguments after \"--\" is [$#] They are: [$@]"
  echo '++ Test: Looping through "$@"'
  for a in "$@"; do
    echo "  ++ [$a]"
  done
  #----------------------------------------------------------------------
  
}

################################### M A I N ########################
#  If you remove "function UseGetOpt () {" and corresponding "}",
#+ you can uncomment the "exit 0" line below, and invoke this script
#+ with the various options from the command-line.
#-------------------------------------------------------------------
# exit 0

echo "Test 1"
UseGetOpt -f myfile one "two three" four

echo;echo "Test 2"
UseGetOpt -h

echo;echo "Test 3 - Short Options"
UseGetOpt -adltf myfile  anotherfile

echo;echo "Test 4 - Long Options"
UseGetOpt --aoption --debug --log --test --file myfile anotherfile

exit

To end this section, a review of the basics . . . and more.

Example A-50. Basics Reviewed

#!/bin/bash
# basics-reviewed.bash

# File extension == *.bash == specific to Bash

#   Copyright (c) Michael S. Zick, 2003; All rights reserved.
#   License: Use in any form, for any purpose.
#   Revision: $ID$
#
#              Edited for layout by M.C.
#   (author of the "Advanced Bash Scripting Guide")
#   Fixes and updates (04/08) by Cliff Bamford.


#  This script tested under Bash versions 2.04, 2.05a and 2.05b.
#  It may not work with earlier versions.
#  This demonstration script generates one --intentional--
#+ "command not found" error message. See line 436.

#  The current Bash maintainer, Chet Ramey, has fixed the items noted
#+ for later versions of Bash.



        ###-------------------------------------------###
        ###  Pipe the output of this script to 'more' ###
        ###+ else it will scroll off the page.        ###
        ###                                           ###
        ###  You may also redirect its output         ###
        ###+ to a file for examination.               ###  
        ###-------------------------------------------###



#  Most of the following points are described at length in
#+ the text of the foregoing "Advanced Bash Scripting Guide."
#  This demonstration script is mostly just a reorganized presentation.
#      -- msz

# Variables are not typed unless otherwise specified.

#  Variables are named. Names must contain a non-digit.
#  File descriptor names (as in, for example: 2>&1)
#+ contain ONLY digits.

# Parameters and Bash array elements are numbered.
# (Parameters are very similar to Bash arrays.)

# A variable name may be undefined (null reference).
unset VarNull

# A variable name may be defined but empty (null contents).
VarEmpty=''                         # Two, adjacent, single quotes.

# A variable name may be defined and non-empty.
VarSomething='Literal'

# A variable may contain:
#   * A whole number as a signed 32-bit (or larger) integer
#   * A string
# A variable may also be an array.

#  A string may contain embedded blanks and may be treated
#+ as if it where a function name with optional arguments.

#  The names of variables and the names of functions
#+ are in different namespaces.


#  A variable may be defined as a Bash array either explicitly or
#+ implicitly by the syntax of the assignment statement.
#  Explicit:
declare -a ArrayVar



# The echo command is a built-in.
echo $VarSomething

# The printf command is a built-in.
# Translate %s as: String-Format
printf %s $VarSomething         # No linebreak specified, none output.
echo                            # Default, only linebreak output.




# The Bash parser word breaks on whitespace.
# Whitespace, or the lack of it is significant.
# (This holds true in general; there are, of course, exceptions.)




# Translate the DOLLAR_SIGN character as: Content-Of.

# Extended-Syntax way of writing Content-Of:
echo ${VarSomething}

#  The ${ ... } Extended-Syntax allows more than just the variable
#+ name to be specified.
#  In general, $VarSomething can always be written as: ${VarSomething}.

# Call this script with arguments to see the following in action.



#  Outside of double-quotes, the special characters @ and *
#+ specify identical behavior.
#  May be pronounced as: All-Elements-Of.

#  Without specification of a name, they refer to the
#+ pre-defined parameter Bash-Array.



# Glob-Pattern references
echo $*                         # All parameters to script or function
echo ${*}                       # Same

# Bash disables filename expansion for Glob-Patterns.
# Only character matching is active.


# All-Elements-Of references
echo $@                         # Same as above
echo ${@}                       # Same as above




#  Within double-quotes, the behavior of Glob-Pattern references
#+ depends on the setting of IFS (Input Field Separator).
#  Within double-quotes, All-Elements-Of references behave the same.


#  Specifying only the name of a variable holding a string refers
#+ to all elements (characters) of a string.


#  To specify an element (character) of a string,
#+ the Extended-Syntax reference notation (see below) MAY be used.




#  Specifying only the name of a Bash array references
#+ the subscript zero element,
#+ NOT the FIRST DEFINED nor the FIRST WITH CONTENTS element.

#  Additional qualification is needed to reference other elements,
#+ which means that the reference MUST be written in Extended-Syntax.
#  The general form is: ${name[subscript]}.

#  The string forms may also be used: ${name:subscript}
#+ for Bash-Arrays when referencing the subscript zero element.


# Bash-Arrays are implemented internally as linked lists,
#+ not as a fixed area of storage as in some programming languages.


#   Characteristics of Bash arrays (Bash-Arrays):
#   --------------------------------------------

#   If not otherwise specified, Bash-Array subscripts begin with
#+  subscript number zero. Literally: [0]
#   This is called zero-based indexing.
###
#   If not otherwise specified, Bash-Arrays are subscript packed
#+  (sequential subscripts without subscript gaps).
###
#   Negative subscripts are not allowed.
###
#   Elements of a Bash-Array need not all be of the same type.
###
#   Elements of a Bash-Array may be undefined (null reference).
#       That is, a Bash-Array may be "subscript sparse."
###
#   Elements of a Bash-Array may be defined and empty (null contents).
###
#   Elements of a Bash-Array may contain:
#     * A whole number as a signed 32-bit (or larger) integer
#     * A string
#     * A string formated so that it appears to be a function name
#     + with optional arguments
###
#   Defined elements of a Bash-Array may be undefined (unset).
#       That is, a subscript packed Bash-Array may be changed
#   +   into a subscript sparse Bash-Array.
###
#   Elements may be added to a Bash-Array by defining an element
#+  not previously defined.
###
# For these reasons, I have been calling them "Bash-Arrays".
# I'll return to the generic term "array" from now on.
#     -- msz


echo "========================================================="

#  Lines 202 - 334 supplied by Cliff Bamford. (Thanks!)
#  Demo --- Interaction with Arrays, quoting, IFS, echo, * and @   ---  
#+ all affect how things work

ArrayVar[0]='zero'                    # 0 normal
ArrayVar[1]=one                       # 1 unquoted literal
ArrayVar[2]='two'                     # 2 normal
ArrayVar[3]='three'                   # 3 normal
ArrayVar[4]='I am four'               # 4 normal with spaces
ArrayVar[5]='five'                    # 5 normal
unset ArrayVar[6]                     # 6 undefined
ArrayValue[7]='seven'                 # 7 normal
ArrayValue[8]=''                      # 8 defined but empty
ArrayValue[9]='nine'                  # 9 normal


echo '--- Here is the array we are using for this test'
echo
echo "ArrayVar[0]='zero'             # 0 normal"
echo "ArrayVar[1]=one                # 1 unquoted literal"
echo "ArrayVar[2]='two'              # 2 normal"
echo "ArrayVar[3]='three'            # 3 normal"
echo "ArrayVar[4]='I am four'        # 4 normal with spaces"
echo "ArrayVar[5]='five'             # 5 normal"
echo "unset ArrayVar[6]              # 6 undefined"
echo "ArrayValue[7]='seven'          # 7 normal"
echo "ArrayValue[8]=''               # 8 defined but empty"
echo "ArrayValue[9]='nine'           # 9 normal"
echo


echo
echo '---Case0: No double-quotes, Default IFS of space,tab,newline ---'
IFS=$'\x20'$'\x09'$'\x0A'            # In exactly this order.
echo 'Here is: printf %q {${ArrayVar[*]}'
printf %q ${ArrayVar[*]}
echo
echo 'Here is: printf %q {${ArrayVar[@]}'
printf %q ${ArrayVar[@]}
echo
echo 'Here is: echo ${ArrayVar[*]}'
echo  ${ArrayVar[@]}
echo 'Here is: echo {${ArrayVar[@]}'
echo ${ArrayVar[@]}

echo
echo '---Case1: Within double-quotes - Default IFS of space-tab- 
newline ---'
IFS=$'\x20'$'\x09'$'\x0A'	    #  These three bytes,
echo 'Here is: printf %q "{${ArrayVar[*]}"'
printf %q "${ArrayVar[*]}"
echo
echo 'Here is: printf %q "{${ArrayVar[@]}"'
printf %q "${ArrayVar[@]}"
echo
echo 'Here is: echo "${ArrayVar[*]}"'
echo  "${ArrayVar[@]}"
echo 'Here is: echo "{${ArrayVar[@]}"'
echo "${ArrayVar[@]}"

echo
echo '---Case2: Within double-quotes - IFS is q'
IFS='q'
echo 'Here is: printf %q "{${ArrayVar[*]}"'
printf %q "${ArrayVar[*]}"
echo
echo 'Here is: printf %q "{${ArrayVar[@]}"'
printf %q "${ArrayVar[@]}"
echo
echo 'Here is: echo "${ArrayVar[*]}"'
echo  "${ArrayVar[@]}"
echo 'Here is: echo "{${ArrayVar[@]}"'
echo "${ArrayVar[@]}"

echo
echo '---Case3: Within double-quotes - IFS is ^'
IFS='^'
echo 'Here is: printf %q "{${ArrayVar[*]}"'
printf %q "${ArrayVar[*]}"
echo
echo 'Here is: printf %q "{${ArrayVar[@]}"'
printf %q "${ArrayVar[@]}"
echo
echo 'Here is: echo "${ArrayVar[*]}"'
echo  "${ArrayVar[@]}"
echo 'Here is: echo "{${ArrayVar[@]}"'
echo "${ArrayVar[@]}"

echo
echo '---Case4: Within double-quotes - IFS is ^ followed by  
space,tab,newline'
IFS=$'^'$'\x20'$'\x09'$'\x0A'       # ^ + space tab newline
echo 'Here is: printf %q "{${ArrayVar[*]}"'
printf %q "${ArrayVar[*]}"
echo
echo 'Here is: printf %q "{${ArrayVar[@]}"'
printf %q "${ArrayVar[@]}"
echo
echo 'Here is: echo "${ArrayVar[*]}"'
echo  "${ArrayVar[@]}"
echo 'Here is: echo "{${ArrayVar[@]}"'
echo "${ArrayVar[@]}"

echo
echo '---Case6: Within double-quotes - IFS set and empty '
IFS=''
echo 'Here is: printf %q "{${ArrayVar[*]}"'
printf %q "${ArrayVar[*]}"
echo
echo 'Here is: printf %q "{${ArrayVar[@]}"'
printf %q "${ArrayVar[@]}"
echo
echo 'Here is: echo "${ArrayVar[*]}"'
echo  "${ArrayVar[@]}"
echo 'Here is: echo "{${ArrayVar[@]}"'
echo "${ArrayVar[@]}"

echo
echo '---Case7: Within double-quotes - IFS is unset'
unset IFS
echo 'Here is: printf %q "{${ArrayVar[*]}"'
printf %q "${ArrayVar[*]}"
echo
echo 'Here is: printf %q "{${ArrayVar[@]}"'
printf %q "${ArrayVar[@]}"
echo
echo 'Here is: echo "${ArrayVar[*]}"'
echo  "${ArrayVar[@]}"
echo 'Here is: echo "{${ArrayVar[@]}"'
echo "${ArrayVar[@]}"

echo
echo '---End of Cases---'
echo "========================================================="; echo



# Put IFS back to the default.
# Default is exactly these three bytes.
IFS=$'\x20'$'\x09'$'\x0A'           # In exactly this order.

# Interpretation of the above outputs:
#   A Glob-Pattern is I/O; the setting of IFS matters.
###
#   An All-Elements-Of does not consider IFS settings.
###
#   Note the different output using the echo command and the
#+  quoted format operator of the printf command.


#  Recall:
#   Parameters are similar to arrays and have the similar behaviors.
###
#  The above examples demonstrate the possible variations.
#  To retain the shape of a sparse array, additional script
#+ programming is required.
###
#  The source code of Bash has a routine to output the
#+ [subscript]=value   array assignment format.
#  As of version 2.05b, that routine is not used,
#+ but that might change in future releases.



# The length of a string, measured in non-null elements (characters):
echo
echo '- - Non-quoted references - -'
echo 'Non-Null character count: '${#VarSomething}' characters.'

# test='Lit'$'\x00''eral'           # $'\x00' is a null character.
# echo ${#test}                     # See that?



#  The length of an array, measured in defined elements,
#+ including null content elements.
echo
echo 'Defined content count: '${#ArrayVar[@]}' elements.'
# That is NOT the maximum subscript (4).
# That is NOT the range of the subscripts (1 . . 4 inclusive).
# It IS the length of the linked list.
###
#  Both the maximum subscript and the range of the subscripts may
#+ be found with additional script programming.

# The length of a string, measured in non-null elements (characters):
echo
echo '- - Quoted, Glob-Pattern references - -'
echo 'Non-Null character count: '"${#VarSomething}"' characters.'

#  The length of an array, measured in defined elements,
#+ including null-content elements.
echo
echo 'Defined element count: '"${#ArrayVar[*]}"' elements.'

#  Interpretation: Substitution does not effect the ${# ... } operation.
#  Suggestion:
#  Always use the All-Elements-Of character
#+ if that is what is intended (independence from IFS).



#  Define a simple function.
#  I include an underscore in the name
#+ to make it distinctive in the examples below.
###
#  Bash separates variable names and function names
#+ in different namespaces.
#  The Mark-One eyeball isn't that advanced.
###
_simple() {
    echo -n 'SimpleFunc'$@          #  Newlines are swallowed in
}                                   #+ result returned in any case.


# The ( ... ) notation invokes a command or function.
# The $( ... ) notation is pronounced: Result-Of.


# Invoke the function _simple
echo
echo '- - Output of function _simple - -'
_simple                             # Try passing arguments.
echo
# or
(_simple)                           # Try passing arguments.
echo

echo '- Is there a variable of that name? -'
echo $_simple not defined           # No variable by that name.

# Invoke the result of function _simple (Error msg intended)

###
$(_simple)                          # Gives an error message:
#                          line 436: SimpleFunc: command not found
#                          ---------------------------------------

echo
###

#  The first word of the result of function _simple
#+ is neither a valid Bash command nor the name of a defined function.
###
# This demonstrates that the output of _simple is subject to evaluation.
###
# Interpretation:
#   A function can be used to generate in-line Bash commands.


# A simple function where the first word of result IS a bash command:
###
_print() {
    echo -n 'printf %q '$@
}

echo '- - Outputs of function _print - -'
_print parm1 parm2                  # An Output NOT A Command.
echo

$(_print parm1 parm2)               #  Executes: printf %q parm1 parm2
                                    #  See above IFS examples for the
                                    #+ various possibilities.
echo

$(_print $VarSomething)             # The predictable result.
echo



# Function variables
# ------------------

echo
echo '- - Function variables - -'
# A variable may represent a signed integer, a string or an array.
# A string may be used like a function name with optional arguments.

# set -vx                           #  Enable if desired
declare -f funcVar                  #+ in namespace of functions

funcVar=_print                      # Contains name of function.
$funcVar parm1                      # Same as _print at this point.
echo

funcVar=$(_print )                  # Contains result of function.
$funcVar                            # No input, No output.
$funcVar $VarSomething              # The predictable result.
echo

funcVar=$(_print $VarSomething)     #  $VarSomething replaced HERE.
$funcVar                            #  The expansion is part of the
echo                                #+ variable contents.

funcVar="$(_print $VarSomething)"   #  $VarSomething replaced HERE.
$funcVar                            #  The expansion is part of the
echo                                #+ variable contents.

#  The difference between the unquoted and the double-quoted versions
#+ above can be seen in the "protect_literal.sh" example.
#  The first case above is processed as two, unquoted, Bash-Words.
#  The second case above is processed as one, quoted, Bash-Word.




# Delayed replacement
# -------------------

echo
echo '- - Delayed replacement - -'
funcVar="$(_print '$VarSomething')" # No replacement, single Bash-Word.
eval $funcVar                       # $VarSomething replaced HERE.
echo

VarSomething='NewThing'
eval $funcVar                       # $VarSomething replaced HERE.
echo

# Restore the original setting trashed above.
VarSomething=Literal

#  There are a pair of functions demonstrated in the
#+ "protect_literal.sh" and "unprotect_literal.sh" examples.
#  These are general purpose functions for delayed replacement literals
#+ containing variables.





# REVIEW:
# ------

#  A string can be considered a Classic-Array of elements (characters).
#  A string operation applies to all elements (characters) of the string
#+ (in concept, anyway).
###
#  The notation: ${array_name[@]} represents all elements of the
#+ Bash-Array: array_name.
###
#  The Extended-Syntax string operations can be applied to all
#+ elements of an array.
###
#  This may be thought of as a For-Each operation on a vector of strings.
###
#  Parameters are similar to an array.
#  The initialization of a parameter array for a script
#+ and a parameter array for a function only differ
#+ in the initialization of ${0}, which never changes its setting.
###
#  Subscript zero of the script's parameter array contains
#+ the name of the script.
###
#  Subscript zero of a function's parameter array DOES NOT contain
#+ the name of the function.
#  The name of the current function is accessed by the $FUNCNAME variable.
###
#  A quick, review list follows (quick, not short).

echo
echo '- - Test (but not change) - -'
echo '- null reference -'
echo -n ${VarNull-'NotSet'}' '          # NotSet
echo ${VarNull}                         # NewLine only
echo -n ${VarNull:-'NotSet'}' '         # NotSet
echo ${VarNull}                         # Newline only

echo '- null contents -'
echo -n ${VarEmpty-'Empty'}' '          # Only the space
echo ${VarEmpty}                        # Newline only
echo -n ${VarEmpty:-'Empty'}' '         # Empty
echo ${VarEmpty}                        # Newline only

echo '- contents -'
echo ${VarSomething-'Content'}          # Literal
echo ${VarSomething:-'Content'}         # Literal

echo '- Sparse Array -'
echo ${ArrayVar[@]-'not set'}

# ASCII-Art time
# State     Y==yes, N==no
#           -       :-
# Unset     Y       Y       ${# ... } == 0
# Empty     N       Y       ${# ... } == 0
# Contents  N       N       ${# ... } > 0

#  Either the first and/or the second part of the tests
#+ may be a command or a function invocation string.
echo
echo '- - Test 1 for undefined - -'
declare -i t
_decT() {
    t=$t-1
}

# Null reference, set: t == -1
t=${#VarNull}                           # Results in zero.
${VarNull- _decT }                      # Function executes, t now -1.
echo $t

# Null contents, set: t == 0
t=${#VarEmpty}                          # Results in zero.
${VarEmpty- _decT }                     # _decT function NOT executed.
echo $t

# Contents, set: t == number of non-null characters
VarSomething='_simple'                  # Set to valid function name.
t=${#VarSomething}                      # non-zero length
${VarSomething- _decT }                 # Function _simple executed.
echo $t                                 # Note the Append-To action.

# Exercise: clean up that example.
unset t
unset _decT
VarSomething=Literal

echo
echo '- - Test and Change - -'
echo '- Assignment if null reference -'
echo -n ${VarNull='NotSet'}' '          # NotSet NotSet
echo ${VarNull}
unset VarNull

echo '- Assignment if null reference -'
echo -n ${VarNull:='NotSet'}' '         # NotSet NotSet
echo ${VarNull}
unset VarNull

echo '- No assignment if null contents -'
echo -n ${VarEmpty='Empty'}' '          # Space only
echo ${VarEmpty}
VarEmpty=''

echo '- Assignment if null contents -'
echo -n ${VarEmpty:='Empty'}' '         # Empty Empty
echo ${VarEmpty}
VarEmpty=''

echo '- No change if already has contents -'
echo ${VarSomething='Content'}          # Literal
echo ${VarSomething:='Content'}         # Literal


# "Subscript sparse" Bash-Arrays
###
#  Bash-Arrays are subscript packed, beginning with
#+ subscript zero unless otherwise specified.
###
#  The initialization of ArrayVar was one way
#+ to "otherwise specify".  Here is the other way:
###
echo
declare -a ArraySparse
ArraySparse=( [1]=one [2]='' [4]='four' )
# [0]=null reference, [2]=null content, [3]=null reference

echo '- - Array-Sparse List - -'
# Within double-quotes, default IFS, Glob-Pattern

IFS=$'\x20'$'\x09'$'\x0A'
printf %q "${ArraySparse[*]}"
echo

#  Note that the output does not distinguish between "null content"
#+ and "null reference".
#  Both print as escaped whitespace.
###
#  Note also that the output does NOT contain escaped whitespace
#+ for the "null reference(s)" prior to the first defined element.
###
# This behavior of 2.04, 2.05a and 2.05b has been reported
#+ and may change in a future version of Bash.

#  To output a sparse array and maintain the [subscript]=value
#+ relationship without change requires a bit of programming.
#  One possible code fragment:
###
# local l=${#ArraySparse[@]}        # Count of defined elements
# local f=0                         # Count of found subscripts
# local i=0                         # Subscript to test
(                                   # Anonymous in-line function
    for (( l=${#ArraySparse[@]}, f = 0, i = 0 ; f < l ; i++ ))
    do
        # 'if defined then...'
        ${ArraySparse[$i]+ eval echo '\ ['$i']='${ArraySparse[$i]} ; (( f++ )) }
    done
)

# The reader coming upon the above code fragment cold
#+ might want to review "command lists" and "multiple commands on a line"
#+ in the text of the foregoing "Advanced Bash Scripting Guide."
###
#  Note:
#  The "read -a array_name" version of the "read" command
#+ begins filling array_name at subscript zero.
#  ArraySparse does not define a value at subscript zero.
###
#  The user needing to read/write a sparse array to either
#+ external storage or a communications socket must invent
#+ a read/write code pair suitable for their purpose.
###
# Exercise: clean it up.

unset ArraySparse

echo
echo '- - Conditional alternate (But not change)- -'
echo '- No alternate if null reference -'
echo -n ${VarNull+'NotSet'}' '
echo ${VarNull}
unset VarNull

echo '- No alternate if null reference -'
echo -n ${VarNull:+'NotSet'}' '
echo ${VarNull}
unset VarNull

echo '- Alternate if null contents -'
echo -n ${VarEmpty+'Empty'}' '              # Empty
echo ${VarEmpty}
VarEmpty=''

echo '- No alternate if null contents -'
echo -n ${VarEmpty:+'Empty'}' '             # Space only
echo ${VarEmpty}
VarEmpty=''

echo '- Alternate if already has contents -'

# Alternate literal
echo -n ${VarSomething+'Content'}' '        # Content Literal
echo ${VarSomething}

# Invoke function
echo -n ${VarSomething:+ $(_simple) }' '    # SimpleFunc Literal
echo ${VarSomething}
echo

echo '- - Sparse Array - -'
echo ${ArrayVar[@]+'Empty'}                 # An array of 'Empty'(ies)
echo

echo '- - Test 2 for undefined - -'

declare -i t
_incT() {
    t=$t+1
}

#  Note:
#  This is the same test used in the sparse array
#+ listing code fragment.

# Null reference, set: t == -1
t=${#VarNull}-1                     # Results in minus-one.
${VarNull+ _incT }                  # Does not execute.
echo $t' Null reference'

# Null contents, set: t == 0
t=${#VarEmpty}-1                    # Results in minus-one.
${VarEmpty+ _incT }                 # Executes.
echo $t'  Null content'

# Contents, set: t == (number of non-null characters)
t=${#VarSomething}-1                # non-null length minus-one
${VarSomething+ _incT }             # Executes.
echo $t'  Contents'

# Exercise: clean up that example.
unset t
unset _incT

# ${name?err_msg} ${name:?err_msg}
#  These follow the same rules but always exit afterwards
#+ if an action is specified following the question mark.
#  The action following the question mark may be a literal
#+ or a function result.
###
#  ${name?} ${name:?} are test-only, the return can be tested.




# Element operations
# ------------------

echo
echo '- - Trailing sub-element selection - -'

#  Strings, Arrays and Positional parameters

#  Call this script with multiple arguments
#+ to see the parameter selections.

echo '- All -'
echo ${VarSomething:0}              # all non-null characters
echo ${ArrayVar[@]:0}               # all elements with content
echo ${@:0}                         # all parameters with content;
                                    # ignoring parameter[0]

echo
echo '- All after -'
echo ${VarSomething:1}              # all non-null after character[0]
echo ${ArrayVar[@]:1}               # all after element[0] with content
echo ${@:2}                         # all after param[1] with content

echo
echo '- Range after -'
echo ${VarSomething:4:3}            # ral
                                    # Three characters after
                                    # character[3]

echo '- Sparse array gotch -'
echo ${ArrayVar[@]:1:2}     #  four - The only element with content.
                            #  Two elements after (if that many exist).
                            #  the FIRST WITH CONTENTS
                            #+ (the FIRST WITH  CONTENTS is being
                            #+ considered as if it
                            #+ were subscript zero).
#  Executed as if Bash considers ONLY array elements with CONTENT
#  printf %q "${ArrayVar[@]:0:3}"    # Try this one

#  In versions 2.04, 2.05a and 2.05b,
#+ Bash does not handle sparse arrays as expected using this notation.
#
#  The current Bash maintainer, Chet Ramey, has corrected this.


echo '- Non-sparse array -'
echo ${@:2:2}               # Two parameters following parameter[1]

# New victims for string vector examples:
stringZ=abcABC123ABCabc
arrayZ=( abcabc ABCABC 123123 ABCABC abcabc )
sparseZ=( [1]='abcabc' [3]='ABCABC' [4]='' [5]='123123' )

echo
echo ' - - Victim string - -'$stringZ'- - '
echo ' - - Victim array - -'${arrayZ[@]}'- - '
echo ' - - Sparse array - -'${sparseZ[@]}'- - '
echo ' - [0]==null ref, [2]==null ref, [4]==null content - '
echo ' - [1]=abcabc [3]=ABCABC [5]=123123 - '
echo ' - non-null-reference count: '${#sparseZ[@]}' elements'

echo
echo '- - Prefix sub-element removal - -'
echo '- - Glob-Pattern match must include the first character. - -'
echo '- - Glob-Pattern may be a literal or a function result. - -'
echo


# Function returning a simple, Literal, Glob-Pattern
_abc() {
    echo -n 'abc'
}

echo '- Shortest prefix -'
echo ${stringZ#123}                 # Unchanged (not a prefix).
echo ${stringZ#$(_abc)}             # ABC123ABCabc
echo ${arrayZ[@]#abc}               # Applied to each element.

# echo ${sparseZ[@]#abc}            # Version-2.05b core dumps.
# Has since been fixed by Chet Ramey.

# The -it would be nice- First-Subscript-Of
# echo ${#sparseZ[@]#*}             # This is NOT valid Bash.

echo
echo '- Longest prefix -'
echo ${stringZ##1*3}                # Unchanged (not a prefix)
echo ${stringZ##a*C}                # abc
echo ${arrayZ[@]##a*c}              # ABCABC 123123 ABCABC

# echo ${sparseZ[@]##a*c}           # Version-2.05b core dumps.
# Has since been fixed by Chet Ramey.

echo
echo '- - Suffix sub-element removal - -'
echo '- - Glob-Pattern match must include the last character. - -'
echo '- - Glob-Pattern may be a literal or a function result. - -'
echo
echo '- Shortest suffix -'
echo ${stringZ%1*3}                 # Unchanged (not a suffix).
echo ${stringZ%$(_abc)}             # abcABC123ABC
echo ${arrayZ[@]%abc}               # Applied to each element.

# echo ${sparseZ[@]%abc}            # Version-2.05b core dumps.
# Has since been fixed by Chet Ramey.

# The -it would be nice- Last-Subscript-Of
# echo ${#sparseZ[@]%*}             # This is NOT valid Bash.

echo
echo '- Longest suffix -'
echo ${stringZ%%1*3}                # Unchanged (not a suffix)
echo ${stringZ%%b*c}                # a
echo ${arrayZ[@]%%b*c}              # a ABCABC 123123 ABCABC a

# echo ${sparseZ[@]%%b*c}           # Version-2.05b core dumps.
# Has since been fixed by Chet Ramey.

echo
echo '- - Sub-element replacement - -'
echo '- - Sub-element at any location in string. - -'
echo '- - First specification is a Glob-Pattern - -'
echo '- - Glob-Pattern may be a literal or Glob-Pattern function result. - -'
echo '- - Second specification may be a literal or function result. - -'
echo '- - Second specification may be unspecified. Pronounce that'
echo '    as: Replace-With-Nothing (Delete) - -'
echo



# Function returning a simple, Literal, Glob-Pattern
_123() {
    echo -n '123'
}

echo '- Replace first occurrence -'
echo ${stringZ/$(_123)/999}         # Changed (123 is a component).
echo ${stringZ/ABC/xyz}             # xyzABC123ABCabc
echo ${arrayZ[@]/ABC/xyz}           # Applied to each element.
echo ${sparseZ[@]/ABC/xyz}          # Works as expected.

echo
echo '- Delete first occurrence -'
echo ${stringZ/$(_123)/}
echo ${stringZ/ABC/}
echo ${arrayZ[@]/ABC/}
echo ${sparseZ[@]/ABC/}

#  The replacement need not be a literal,
#+ since the result of a function invocation is allowed.
#  This is general to all forms of replacement.
echo
echo '- Replace first occurrence with Result-Of -'
echo ${stringZ/$(_123)/$(_simple)}  # Works as expected.
echo ${arrayZ[@]/ca/$(_simple)}     # Applied to each element.
echo ${sparseZ[@]/ca/$(_simple)}    # Works as expected.

echo
echo '- Replace all occurrences -'
echo ${stringZ//[b2]/X}             # X-out b's and 2's
echo ${stringZ//abc/xyz}            # xyzABC123ABCxyz
echo ${arrayZ[@]//abc/xyz}          # Applied to each element.
echo ${sparseZ[@]//abc/xyz}         # Works as expected.

echo
echo '- Delete all occurrences -'
echo ${stringZ//[b2]/}
echo ${stringZ//abc/}
echo ${arrayZ[@]//abc/}
echo ${sparseZ[@]//abc/}

echo
echo '- - Prefix sub-element replacement - -'
echo '- - Match must include the first character. - -'
echo

echo '- Replace prefix occurrences -'
echo ${stringZ/#[b2]/X}             # Unchanged (neither is a prefix).
echo ${stringZ/#$(_abc)/XYZ}        # XYZABC123ABCabc
echo ${arrayZ[@]/#abc/XYZ}          # Applied to each element.
echo ${sparseZ[@]/#abc/XYZ}         # Works as expected.

echo
echo '- Delete prefix occurrences -'
echo ${stringZ/#[b2]/}
echo ${stringZ/#$(_abc)/}
echo ${arrayZ[@]/#abc/}
echo ${sparseZ[@]/#abc/}

echo
echo '- - Suffix sub-element replacement - -'
echo '- - Match must include the last character. - -'
echo

echo '- Replace suffix occurrences -'
echo ${stringZ/%[b2]/X}             # Unchanged (neither is a suffix).
echo ${stringZ/%$(_abc)/XYZ}        # abcABC123ABCXYZ
echo ${arrayZ[@]/%abc/XYZ}          # Applied to each element.
echo ${sparseZ[@]/%abc/XYZ}         # Works as expected.

echo
echo '- Delete suffix occurrences -'
echo ${stringZ/%[b2]/}
echo ${stringZ/%$(_abc)/}
echo ${arrayZ[@]/%abc/}
echo ${sparseZ[@]/%abc/}

echo
echo '- - Special cases of null Glob-Pattern - -'
echo

echo '- Prefix all -'
# null substring pattern means 'prefix'
echo ${stringZ/#/NEW}               # NEWabcABC123ABCabc
echo ${arrayZ[@]/#/NEW}             # Applied to each element.
echo ${sparseZ[@]/#/NEW}            # Applied to null-content also.
                                    # That seems reasonable.

echo
echo '- Suffix all -'
# null substring pattern means 'suffix'
echo ${stringZ/%/NEW}               # abcABC123ABCabcNEW
echo ${arrayZ[@]/%/NEW}             # Applied to each element.
echo ${sparseZ[@]/%/NEW}            # Applied to null-content also.
                                    # That seems reasonable.

echo
echo '- - Special case For-Each Glob-Pattern - -'
echo '- - - - This is a nice-to-have dream - - - -'
echo

_GenFunc() {
    echo -n ${0}                    # Illustration only.
    # Actually, that would be an arbitrary computation.
}

# All occurrences, matching the AnyThing pattern.
# Currently //*/ does not match null-content nor null-reference.
# /#/ and /%/ does match null-content but not null-reference.
echo ${sparseZ[@]//*/$(_GenFunc)}


#  A possible syntax would be to make
#+ the parameter notation used within this construct mean:
#   ${1} - The full element
#   ${2} - The prefix, if any, to the matched sub-element
#   ${3} - The matched sub-element
#   ${4} - The suffix, if any, to the matched sub-element
#
# echo ${sparseZ[@]//*/$(_GenFunc ${3})}   # Same as ${1} here.
# Perhaps it will be implemented in a future version of Bash.


exit 0

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