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GETOPT(1) General Commands Manual GETOPT(1)

getopt — parse command options

args=`getopt optstring $*`

set -- `getopt optstring $*`

getopt 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. getopt 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.

getopt should not be used in new scripts; use the shell builtin getopts instead.

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 [c], which requires an argument.

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 getopt.

getopt prints an error message on the standard error output when it encounters an option letter not included in [optstring].

sh(1), getopt(3)

Written by Henry Spencer, working from a Bell Labs manual page. Behavior believed identical to the Bell version.

Whatever getopt(3) has.

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 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.

November 28, 2009 NetBSD-9.2