Appendix G. 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 script ones.

Table G-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 as CALL)
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 be translated into their UNIX equivalents in order to convert a batch file into a shell script.

Table G-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

Note

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

DOS supports a very limited and incompatible subset of filename wildcard expansion, recognizing only 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 G-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.

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

#!/bin/bash
# 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.