args=`getopt
optstring
$*`
set
--
`getopt
optstring
$*`
args=`getopt abc: $*`
if [ $? -ne 0 ]; then
echo 'Usage: ...'
exit 2
fi
set -- $args
while [ $# -gt 0 ]; do
case "$1" in
-a|-b)
flag=$1
;;
-c)
carg=$2; shift
;;
--)
shift; break
;;
esac
shift
done
This code will accept any of the following as equivalent:
cmd -acarg file file
cmd -a -c arg file file
cmd -carg -a file file
cmd -a -carg -- file file
IEEE Std 1003.2 (``POSIX.2'') mandates that the sh(1) set command return the value of 0 for the exit status. Therefore, the exit status of the getopt command is lost when getopt and the sh(1) set command are used on the same line. The example given is one way to detect errors found by .
Arguments containing white space or embedded shell metacharacters generally will not survive intact; this looks easy to fix but isn't.
The error message for an invalid option is identified as coming from getopt rather than from the shell procedure containing the invocation of ; this again is hard to fix.
The precise best way to use the set command to set the arguments without disrupting the value(s) of shell options varies from one shell version to another.