.\"	$OpenBSD: getopt.1,v 1.20 2021/05/04 21:03:31 naddy Exp $
.\"
.\" This material, written by Henry Spencer, was released by him
.\" into the public domain and is thus not subject to any copyright.
.\"
.Dd $Mdocdate: May 4 2021 $
.Dt GETOPT 1
.Os
.Sh NAME
.Nm getopt
.Nd parse command options
.Sh SYNOPSIS
.Nm
.Ar optstring
.Va $*
.Sh DESCRIPTION
The
.Nm
utility cannot handle option arguments containing whitespace;
consider using the standard
.Ic getopts
shell built-in instead.
.Pp
.Nm
is used to break up options in command lines for easy parsing by
shell procedures, and to check for legal options.
.Ar optstring
is a string of recognized option letters (see
.Xr 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 whitespace.
However, if a letter is followed by two colons, the argument is optional
and may not be separated by whitespace \- this is an extension not
covered by POSIX.
The special option
.Sq --
is used to delimit the end of the options.
.Nm
will place
.Sq --
in the arguments at the end of the options,
or recognize it if used explicitly.
The shell arguments
.Pf ( Va $1 , $2 , ... )
are reset so that each option is
preceded by a
.Sq -
and in its own shell argument;
each option argument is also in its own shell argument.
.Sh EXAMPLES
The following code fragment shows how one might process the arguments
for a command that can take the options
.Fl a
and
.Fl b ,
and the option
.Fl o ,
which requires an argument.
.Bd -literal -offset indent
args=`getopt abo: $*`
if [ $? -ne 0 ]
then
	echo 'Usage: ...'
	exit 2
fi
set -- $args
while [ $# -ne 0 ]
do
	case "$1"
	in
		-a|-b)
			flag="$1"; shift;;
		-o)
			oarg="$2"; shift; shift;;
		--)
			shift; break;;
	esac
done
.Ed
.Pp
This code will accept any of the following as equivalent:
.Bd -literal -offset indent
cmd -aoarg file file
cmd -a -o arg file file
cmd -oarg -a file file
cmd -a -oarg -- file file
.Ed
.Sh DIAGNOSTICS
.Nm
prints an error message on the standard error output when it
encounters an option letter not included in
.Ar optstring .
.Sh SEE ALSO
.Xr sh 1 ,
.Xr getopt 3
.Sh HISTORY
Written by Henry Spencer, working from a Bell Labs manual page.
Behavior believed identical to the Bell version.
.Sh CAVEATS
Note that the construction
.Pp
.Dl set -- `getopt optstring $*`
.Pp
is not recommended, as the exit value from
.Sy set
will prevent the exit value from
.Nm
from being determined.
.Sh BUGS
Whatever
.Xr getopt 3
has.
.Pp
Arguments containing whitespace or embedded shell metacharacters
generally will not survive intact; this looks easy to fix but isn't.
.Pp
The error message for an invalid option is identified as coming
from
.Nm
rather than from the shell procedure containing the invocation
of
.Nm getopt ;
this again is hard to fix.
.Pp
The precise best way to use the
.Sy set
command to set the arguments without disrupting the value(s) of
shell options varies from one shell version to another.