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Index

This index / glossary / quick-reference lists many of the important topics covered in the text. Terms are arranged in approximate ASCII sorting order, modified as necessary for enhanced clarity.

Note that commands are indexed in Part 4.

* * *

^ (caret)

~ Tilde

= Equals sign

< Left angle bracket

> Right angle bracket

| Pipe, a device for passing the output of a command to another command or to the shell

|| Logical OR test operator

- (dash)

; (semicolon)

: Colon, null command, equivalent to the true Bash builtin

! Negation operator, inverts exit status of a test or command

? (question mark)

// Double forward slash, behavior of cd command toward

. (dot / period)

' ... ' (single quotes) strong quoting

" ... " (double quotes) weak quoting

,

() Parentheses

[ Left bracket, test construct

[ ]Brackets

[[ ... ]] Double brackets, extended test construct

$ Anchor, in a Regular Expression

$ Prefix to a variable name

$( ... ) Command substitution, setting a variable with output of a command, using parentheses notation

` ... ` Command substitution, using backquotes notation

$[ ... ] Integer expansion (deprecated)

${ ... } Variable manipulation / evaluation

\ Escape the character following

&

# Hashmark, special symbol beginning a script comment

#! Sha-bang, special string starting a shell script

* Asterisk

% Percent sign

+ Plus sign

* * *

Shell Variables

$_ Last argument to previous command

$- Flags passed to script, using set

$! Process ID of last background job

$? Exit status of a command

$@ All the positional parameters, as separate words

$* All the positional parameters, as a single word

$$ Process ID of the script

$# Number of arguments passed to a function, or to the script itself

$0 Filename of the script

$1 First argument passed to script

$9 Ninth argument passed to script

Table of shell variables

* * * * * *

-a Logical AND compound comparison test

Address database, script example

Advanced Bash Scripting Guide, where to download

Alias

Anagramming

And list

And logical operator &&

Angle brackets, escaped, \< . . . \> word boundary in a Regular Expression

Anonymous here document, using :

Archiving

Arithmetic expansion

Arithmetic operators

Arrays

Arrow keys, detecting

ASCII table

awk field-oriented text processing language

* * *

Backquotes, used in command substitution

Base conversion, example script

Bash

.bashrc

$BASH_SUBSHELL

Basic commands, external

Batch files, DOS

Batch processing

bc, calculator utility

Bibliography

Bison utility

Bitwise operators

Block devices

Blocks of code

Brace expansion

Brackets, [ ]

Brackets, curly, {}, used in

break loop control command

Builtins in Bash

* * *

case construct

cat, concatentate file(s)

Character devices

Checksum

Child processes

Colon, : , equivalent to the true Bash builtin

Colorizing scripts

Comma operator, linking commands or operations

Command-line options

command_not_found_handle () builtin error-handling function (version 4+ of Bash)

Command substitution

Comment headers, special purpose

Commenting out blocks of code

Communications and hosts

Compound comparison operators

Compression utilities

continue loop control command

Control characters

Coprocesses

cron, scheduling daemon

C-style syntax , for handling variables

Crossword puzzle solver

Curly brackets {}

* * *

Daemons, in UNIX-type OS

date

dc, calculator utility

dd, data duplicator command

Debugging scripts

Decimal number, Bash interprets numbers as

declare builtin

Default parameters

/dev directory

Device file

dialog, utility for generating dialog boxes in a script

$DIRSTACK directory stack

Disabled commands, in restricted shells

do keyword, begins execution of commands within a loop

done keyword, terminates a loop

DOS batch files, converting to shell scripts

DOS commands, UNIX equivalents of (table)

dot files, "hidden" setup and configuration files

Double brackets [[ ... ]] test construct

Double parentheses (( ... )) arithmetic expansion/evaluation construct

Double quotes " ... " weak quoting

Double-spacing a text file, using sed

* * *

-e File exists test

echo

elif, Contraction of else and if

else

Encrypting files, using openssl

esac, keyword terminating case construct

Environmental variables

-eq , is-equal-to integer comparison test

Eratosthenes, Sieve of, algorithm for generating prime numbers

Escaped characters, special meanings of

/etc/fstab (filesystem mount) file

/etc/passwd (user account) file

$EUID, Effective user ID

eval, Combine and evaluate expression(s), with variable expansion

Evaluation of octal/hex constants within [[ ... ]]

exec command, using in redirection

Exercises

Exit and Exit status

Export, to make available variables to child processes

expr, Expression evaluator

Extended Regular Expressions

* * *

factor, decomposes an integer into its prime factors

false, returns unsuccessful (1) exit status

Field, a group of characters that comprises an item of data

Files / Archiving

File descriptors

  • Closing

    n<&- Close input file descriptor n

    0<&-, <&- Close stdin

    n>&- Close output file descriptor n

    1>&-, >&- Close stdout

  • File handles in C, similarity to

File encryption

find

Filter

Floating point numbers, Bash does not recognize

fold, a filter to wrap lines of text

Forking a child process

for loops

Functions

* * *

Games and amusements

getopt, external command for parsing script command-line arguments

getopts, Bash builtin for parsing script command-line arguments

Global variable

Globbing, filename expansion

Golden Ratio (Phi)

-ge , greater-than or equal integer comparison test

-gt , greater-than integer comparison test

groff, text markup and formatting language

$GROUPS, Groups user belongs to

gzip, compression utility

* * *

Hashing, creating lookup keys in a table

head, echo to stdout lines at the beginning of a text file

help, gives usage summary of a Bash builtin

Here documents

History commands

$HOME, user's home directory

Homework assignment solver

$HOSTNAME, system host name

* * *

$Id parameter, in rcs (Revision Control System)

if [ condition ]; then ... test construct

$IFS, Internal field separator variable

Integer comparison operators

in, keyword preceding [list] in a for loop

Initialization table, /etc/inittab

Inline group, i.e., code block

Interactive script, test for

I/O redirection

Indirect referencing of variables

Iteration

* * *

Job IDs, table

jot, Emit a sequence of integers. Equivalent to seq.

* * *

Keywords

kill, terminate a process by process ID

killall, terminate a process by name

killall script in /etc/rc.d/init.d

* * *

-le , less-than or equal integer comparison test

let, setting and carrying out arithmetic operations on variables

Limit string, in a here document

$LINENO, variable indicating the line number where it appears in a script

Link, file (using ln command)

List constructs

Local variables

Localization

Logical operators (&&, ||, etc.)

Logout file, the ~/.bash_logout file

Loopback device, mounting a file on a block device

Loops

Loopback devices

-lt , less-than integer comparison test

* * *

m4, macro processing language

$MACHTYPE, Machine type

Magic number, marker at the head of a file indicating the file type

Makefile, file containing the list of dependencies used by make command

man, manual page (lookup)

mapfile builtin, loads an array with a text file

Math commands

Meta-meaning

Modulo, arithmetic remainder operator

Mortgage calculations, example script

* * *

-n String not null test

Named pipe, a temporary FIFO buffer

nc, netcat, a toolkit for TCP and UDP ports

-ne, not-equal-to integer comparison test

Negation operator, !, reverses the sense of a test

netstat, Network statistics

nl, a filter to number lines of text

Noclobber, -C option to Bash to prevent overwriting of files

NOT logical operator, !

null variable assignment, avoiding

* * *

-o Logical OR compound comparison test

octal, base-8 numbers

od, octal dump

$OLDPWD Previous working directory

openssl encryption utility

Operator

Options, passed to shell or script on command line or by set command

Or list

Or logical operator, ||

* * *

Parameter substitution

Parent / child process problem, a child process cannot export variables to a parent process

Parentheses

$PATH, the path (location of system binaries)

Perl, programming language

Perquackey-type anagramming game (Quackey script)

Petals Around the Rose

PID, Process ID, an identification number assigned to a running process.

Pipe, | , a device for passing the output of a command to another command or to the shell

Pitfalls

Pointers

Portability issues in shell scripting

Positional parameters

POSIX, Portable Operating System Interface / UNIX

$PPID, process ID of parent process

Precedence, operator

Prepending lines at head of a file, script example

Prime numbers

printf, formatted print command

/proc directory

Process

Process substitution

Programmable completion (tab expansion)

Prompt

  • $PS1, Main prompt, seen at command line

  • $PS2, Secondary prompt

Pseudo-code, as problem-solving method

$PWD, Current working directory

* * *

Quackey, a Perquackey-type anagramming game (script)

Question mark, ?

Quoting

* * *

Random numbers

rcs

read, set value of a variable from stdin

readline library

Recursion

Redirection

Reference Cards

Regular Expressions

$REPLY, Default value associated with read command

Restricted shell, shell (or script) with certain commands disabled

return, command that terminates a function

run-parts

* * *

Scope of a variable, definition

Script options, set at command line

Scripting routines, library of useful definitions and functions

Secondary prompt, $PS2

Security issues

sed, pattern-based programming language

  • Table, basic operators

  • Table, examples of operators

select, construct for menu building

Semaphore

Semicolon required, when do keyword is on first line of loop

seq, Emit a sequence of integers. Equivalent to jot.

set, Change value of internal script variables

Shell script, definition of

Shell wrapper, script embedding a command or utility

shift, reassigning positional parameters

$SHLVL, shell level, depth to which the shell (or script) is nested

shopt, change shell options

Signal, a message sent to a process

Simulations

Single quotes (' ... ') strong quoting

Socket, a communication node associated with an I/O port

Sorting

source, execute a script or, within a script, import a file

Spam, dealing with

Special characters

Stack

Standard Deviation, example script

Startup files, Bash

stdin and stdout

Stopwatch, example script

Strings

Strong quoting ' ... '

Stylesheet for writing scripts

Subshell

su Substitute user, log on as a different user or as root

suid (set user id) file flag

Symbolic links

Swapfiles

* * *

Tab completion

Table lookup, script example

tail, echo to stdout lines at the (tail) end of a text file

tar, archiving utility

tee, redirect to a file output of command(s) partway through a pipe

Terminals

test command

Test constructs

Test operators

Text and text file processing

Time / Date

Timed input

Tips and hints for Bash scripts

$TMOUT, Timeout interval

Token, a symbol that may expand to a keyword or command

tput, terminal-control command

tr, character translation filter

Trap, specifying an action upon receipt of a signal

Trinary operator, C-style, var>10?88:99

true, returns successful (0) exit status

typeset builtin

* * *

$UID, User ID number

unalias, to remove an alias

uname, output system information

Uninitialized variables

uniq, filter to remove duplicate lines from a sorted file

unset, delete a shell variable

until loop

until [ condition-is-true ]; do

* * *

Variables

* * *

wait, suspend script execution

Weak quoting " ... "

while loop

while [ condition ]; do

Whitespace, spaces, tabs, and newline characters

who, information about logged on users

Widgets

Wild card characters

Word splitting

Wrapper, shell

* * *

xargs, Filter for grouping arguments

* * *

yes

* * *

-z String is null

Zombie, a process that has terminated, but not yet been killed by its parent