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GETOPT(1) General Commands Manual GETOPT(1)

getopt — parse command options

args=`getopt optstring $*` ; errcode=$?; set -- $args

The getopt utility is used to break up options in command lines for easy parsing by shell procedures, and to check for legal options. Optstring is a string of recognized option letters (see getopt(3)); if a letter is followed by a colon, the option is expected to have an argument which may or may not be separated from it by white space. The special option ‘--’ is used to delimit the end of the options. The getopt utility will place ‘--’ in the arguments at the end of the options, or recognize it if used explicitly. The shell arguments ($1 $2 ...) are reset so that each option is preceded by a ‘-’ and in its own shell argument; each option argument is also in its own shell argument.

The getopt utility prints an error message on the standard error output and exits with status > 0 when it encounters an option letter not included in optstring.

The following code fragment shows how one might process the arguments for a command that can take the options -a and -b, and the option -o, which requires an argument.

args=`getopt abo: $*`
# you should not use `getopt abo: "$@"` since that would parse
# the arguments differently from what the set command below does.
if [ $? -ne 0 ]; then
	echo 'Usage: ...'
	exit 2
fi
set -- $args
# You cannot use the set command with a backquoted getopt directly,
# since the exit code from getopt would be shadowed by those of set,
# which is zero by definition.
while :; do
	case "$1" in
	-a|-b)
		echo "flag $1 set"; sflags="${1#-}$sflags"
		shift
		;;
	-o)
		echo "oarg is '$2'"; oarg="$2"
		shift; shift
		;;
	--)
		shift; break
		;;
	esac
done
echo "single-char flags: '$sflags'"
echo "oarg is '$oarg'"

This code will accept any of the following as equivalent:

cmd -aoarg file1 file2
cmd -a -o arg file1 file2
cmd -oarg -a file1 file2
cmd -a -oarg -- file1 file2

getopts(1), sh(1), getopt(3)

Written by Henry Spencer, working from a Bell Labs manual page. Behavior believed identical to the Bell version. Example changed in FreeBSD version 3.2 and 4.0.

Whatever getopt(3) has.

Arguments containing white space or embedded shell metacharacters generally will not survive intact; this looks easy to fix but is not. People trying to fix getopt or the example in this manpage should check the history of this file in FreeBSD.

The error message for an invalid option is identified as coming from getopt rather than from the shell procedure containing the invocation of getopt; 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.

Each shellscript has to carry complex code to parse arguments halfway correctly (like the example presented here). A better getopt-like tool would move much of the complexity into the tool and keep the client shell scripts simpler.

August 1, 2015 macOS