Appendix L. Converting DOS Batch Files to Shell Scripts

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2023-12-01

Quite a number of programmers learned scripting on a PC runningDOS. Even the crippled DOS batch file language allowed writing somefairly powerful scripts and applications, though they often requiredextensive kludges and workarounds. Occasionally, the need stillarises to convert an old DOS batch file to a UNIX shell script. Thisis generally not difficult, as DOS batch file operators are only alimited subset of the equivalent shell scripting ones.

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

Batch File Operator	Shell Script Equivalent	Meaning
`%`	$	command-line parameter prefix
`/`	-	command option flag
`\`	/	directory path separator
`==`	=	(equal-to) string comparison test
`!==!`	!=	(not equal-to) string comparison test
`\|`	\|	pipe
`@`	set `+v`	do not echo current command
`*`	*	filename "wild card"
`>`	>	file redirection (overwrite)
`>>`	>>	file redirection (append)
`<`	<	redirect `stdin`
`%VAR%`	$VAR	environmental variable
`REM`	#	comment
`NOT`	!	negate following test
`NUL`	`/dev/null`	"black hole"for burying command output
`ECHO`	echo	echo (many more option in Bash)
`ECHO.`	echo	echo blank line
`ECHO OFF`	set `+v`	do not echo command(s) following
`FOR %%VAR IN (LIST) DO`	for var in [list]; do	"for"loop
`:LABEL`	none (unnecessary)	label
`GOTO`	none (use a function)	jump to another location in the script
`PAUSE`	sleep	pause or wait an interval
`CHOICE`	case or select	menu choice
`IF`	if	if-test
`IF EXIST FILENAME`	if [ -e filename ]	test if file exists
`IF !%N==!`	if [ -z "$N" ]	if replaceable parameter "N"not present
`CALL`	source or . (dot operator)	"include"another script
`COMMAND /C`	source or . (dot operator)	"include"another script (same asCALL)
`SET`	export	set an environmental variable
`SHIFT`	shift	left shift command-line argument list
`SGN`	-lt or -gt	sign (of integer)
`ERRORLEVEL`	$?	exit status
`CON`	`stdin`	"console"(`stdin`)
`PRN`	`/dev/lp0`	(generic) printer device
`LPT1`	`/dev/lp0`	first printer device
`COM1`	`/dev/ttyS0`	first serial port

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

Table L-2. DOS commands and their UNIX equivalents

DOS Command	UNIX Equivalent	Effect
`ASSIGN`	ln	link file or directory
`ATTRIB`	chmod	change file permissions
`CD`	cd	change directory
`CHDIR`	cd	change directory
`CLS`	clear	clear screen
`COMP`	diff, comm, cmp	file compare
`COPY`	cp	file copy
`Ctl-C`	Ctl-C	break (signal)
`Ctl-Z`	Ctl-D	EOF (end-of-file)
`DEL`	rm	delete file(s)
`DELTREE`	rm -rf	delete directory recursively
`DIR`	ls -l	directory listing
`ERASE`	rm	delete file(s)
`EXIT`	exit	exit current process
`FC`	comm, cmp	file compare
`FIND`	grep	find strings in files
`MD`	mkdir	make directory
`MKDIR`	mkdir	make directory
`MORE`	more	text file paging filter
`MOVE`	mv	move
`PATH`	$PATH	path to executables
`REN`	mv	rename (move)
`RENAME`	mv	rename (move)
`RD`	rmdir	remove directory
`RMDIR`	rmdir	remove directory
`SORT`	sort	sort file
`TIME`	date	display system time
`TYPE`	cat	output file to `stdout`
`XCOPY`	cp	(extended) file copy

Virtually all UNIX and shell operators and commands havemany more options and enhancements than their DOS and batch fileequivalents. Many DOS batch files rely on auxiliary utilities,such as ask.com, a crippled counterpart toread.

DOS supports a very limited and incompatible subset offilename wildcard expansion,recognizing only the*and?characters.

Converting a DOS batch file into a shell script is generallystraightforward, and the result ofttimes reads better than theoriginal.

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

   1 REM VIEWDATA
   2
   3 REM INSPIRED BY AN EXAMPLE IN "DOS POWERTOOLS"
   4 REM                           BY PAUL SOMERSON
   5
   6
   7 @ECHO OFF
   8
   9 IF !%1==! GOTO VIEWDATA
  10 REM  IF NO COMMAND-LINE ARG...
  11 FIND "%1" C:\BOZO\BOOKLIST.TXT
  12 GOTO EXIT0
  13 REM  PRINT LINE WITH STRING MATCH, THEN EXIT.
  14
  15 :VIEWDATA
  16 TYPE C:\BOZO\BOOKLIST.TXT | MORE
  17 REM  SHOW ENTIRE FILE, 1 PAGE AT A TIME.
  18
  19 :EXIT0

The script conversion is somewhat of an improvement.

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

   1 #!/bin/bash
   2 # viewdata.sh
   3 # Conversion of VIEWDATA.BAT to shell script.
   4
   5 DATAFILE=/home/bozo/datafiles/book-collection.data
   6 ARGNO=1
   7
   8 # @ECHO OFF                 Command unnecessary here.
   9
  10 if [ $# -lt "$ARGNO" ]    # IF !%1==! GOTO VIEWDATA
  11 then
  12   less $DATAFILE          # TYPE C:\MYDIR\BOOKLIST.TXT | MORE
  13 else
  14   grep "$1" $DATAFILE     # FIND "%1" C:\MYDIR\BOOKLIST.TXT
  15 fi
  16
  17 exit 0                    # :EXIT0
  18
  19 #  GOTOs, labels, smoke-and-mirrors, and flimflam unnecessary.
  20 #  The converted script is short, sweet, and clean,
  21 #+ which is more than can be said for the original.

Ted Davis' ShellScripts on the PCsite has a set of comprehensivetutorials on the old-fashioned art of batch fileprogramming. Certain of his ingenious techniques could conceivablyhave relevance for shell scripts.