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Appendix L. Converting DOS Batch Files to Shell Scripts

Quite a number of programmers learned scripting on a PC running DOS. Even the crippled DOS batch file language allowed writing some fairly powerful scripts and applications, though they often required extensive kludges and workarounds. Occasionally, the need still arises to convert an old DOS batch file to a UNIX shell script. This is generally not difficult, as DOS batch file operators are only a limited subset of the equivalent shell scripting ones.

Table L-1. Batch file keywords / variables / operators, and their shell equivalents

Batch File OperatorShell Script EquivalentMeaning
%$command-line parameter prefix
/-command option flag
\/directory path separator
===(equal-to) string comparison test
!==!!=(not equal-to) string comparison test
||pipe
@set +vdo not echo current command
**filename "wild card"
>>file redirection (overwrite)
>>>>file redirection (append)
<<redirect stdin
%VAR%$VARenvironmental variable
REM#comment
NOT!negate following test
NUL/dev/null"black hole" for burying command output
ECHOechoecho (many more option in Bash)
ECHO.echoecho blank line
ECHO OFFset +vdo not echo command(s) following
FOR %%VAR IN (LIST) DOfor var in [list]; do"for" loop
:LABELnone (unnecessary)label
GOTOnone (use a function)jump to another location in the script
PAUSEsleeppause or wait an interval
CHOICEcase or selectmenu choice
IFifif-test
IF EXIST FILENAMEif [ -e filename ]test if file exists
IF !%N==!if [ -z "$N" ]if replaceable parameter "N" not present
CALLsource or . (dot operator)"include" another script
COMMAND /Csource or . (dot operator)"include" another script (same as CALL)
SETexportset an environmental variable
SHIFTshiftleft shift command-line argument list
SGN-lt or -gtsign (of integer)
ERRORLEVEL$?exit status
CONstdin"console" (stdin)
PRN/dev/lp0(generic) printer device
LPT1/dev/lp0first printer device
COM1/dev/ttyS0first serial port

Batch files usually contain DOS commands. These must be translated into their UNIX equivalents in order to convert a batch file into a shell script.

Table L-2. DOS commands and their UNIX equivalents

DOS CommandUNIX EquivalentEffect
ASSIGNlnlink file or directory
ATTRIBchmodchange file permissions
CDcdchange directory
CHDIRcdchange directory
CLSclearclear screen
COMPdiff, comm, cmpfile compare
COPYcpfile copy
Ctl-CCtl-Cbreak (signal)
Ctl-ZCtl-DEOF (end-of-file)
DELrmdelete file(s)
DELTREErm -rfdelete directory recursively
DIRls -ldirectory listing
ERASErmdelete file(s)
EXITexitexit current process
FCcomm, cmpfile compare
FINDgrepfind strings in files
MDmkdirmake directory
MKDIRmkdirmake directory
MOREmoretext file paging filter
MOVEmvmove
PATH$PATHpath to executables
RENmvrename (move)
RENAMEmvrename (move)
RDrmdirremove directory
RMDIRrmdirremove directory
SORTsortsort file
TIMEdatedisplay system time
TYPEcatoutput file to stdout
XCOPYcp(extended) file copy

Virtually all UNIX and shell operators and commands have many more options and enhancements than their DOS and batch file counterparts. Many DOS batch files rely on auxiliary utilities, such as ask.com, a crippled counterpart to read.

DOS supports only a very limited and incompatible subset of filename wild-card expansion, recognizing just the * and ? characters.

Converting a DOS batch file into a shell script is generally straightforward, and the result ofttimes reads better than the original.

Example L-1. VIEWDATA.BAT: DOS Batch File

REM VIEWDATA

REM INSPIRED BY AN EXAMPLE IN "DOS POWERTOOLS"
REM                           BY PAUL SOMERSON


@ECHO OFF

IF !%1==! GOTO VIEWDATA
REM  IF NO COMMAND-LINE ARG...
FIND "%1" C:\BOZO\BOOKLIST.TXT
GOTO EXIT0
REM  PRINT LINE WITH STRING MATCH, THEN EXIT.

:VIEWDATA
TYPE C:\BOZO\BOOKLIST.TXT | MORE
REM  SHOW ENTIRE FILE, 1 PAGE AT A TIME.

:EXIT0

The script conversion is somewhat of an improvement. [1]

Example L-2. viewdata.sh: Shell Script Conversion of VIEWDATA.BAT

#!/bin/bash
# viewdata.sh
# Conversion of VIEWDATA.BAT to shell script.

DATAFILE=/home/bozo/datafiles/book-collection.data
ARGNO=1

# @ECHO OFF                 Command unnecessary here.

if [ $# -lt "$ARGNO" ]    # IF !%1==! GOTO VIEWDATA
then
  less $DATAFILE          # TYPE C:\MYDIR\BOOKLIST.TXT | MORE
else
  grep "$1" $DATAFILE     # FIND "%1" C:\MYDIR\BOOKLIST.TXT
fi  

exit 0                    # :EXIT0

#  GOTOs, labels, smoke-and-mirrors, and flimflam unnecessary.
#  The converted script is short, sweet, and clean,
#+ which is more than can be said for the original.

Ted Davis' Shell Scripts on the PC site has a set of comprehensive tutorials on the old-fashioned art of batch file programming. Certain of his ingenious techniques could conceivably have relevance for shell scripts.

Notes

[1]

Various readers have suggested modifications of the above batch file to prettify it and make it more compact and efficient. In the opinion of the ABS Guide author, this is wasted effort. A Bash script can access a DOS filesystem, or even an NTFS partition (with the help of ntfs-3g) to do batch or scripted operations.


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