freebsd/usr.bin/getopt/getopt.1

.\" $FreeBSD$
.\"
.Dd April 3, 1999
.Dt GETOPT 1
.Os
.Sh NAME
.Nm getopt
.Nd parse command options
.Sh SYNOPSIS
.Nm args=\`getopt Ar optstring $*\`
; errcode=$?; set \-\- $args
.Sh DESCRIPTION
.Nm Getopt
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 white space.
The special option
.Ql \-\-
is used to delimit the end of the options.
.Nm Getopt
will place
.Ql \-\-
in the arguments at the end of the options,
or recognize it if used explicitly.
The shell arguments
(\fB$1 $2\fR ...) are reset so that each option is
preceded by a
.Ql \-
and in its own shell argument;
each option argument is also in its own shell argument.
.Sh EXAMPLE
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.
.Pp
.Bd -literal -offset indent
args=\`getopt abo: $*\`
# you should not use \`getopt abo: "$@"\` since that would parse
# the arguments differently from what the set command below does.
if [ $? != 0 ]
then
	echo 'Usage: ...'
	exit 2
fi
set \-\- $args
# You cannot use the set command with a backquoted getopt directly,
# since the exit code from getopt would be shadowed by those of set, 
# which is zero by definition.
for i
do
	case "$i"
	in
		\-a|\-b)
			echo flag $i set; sflags="${i#-}$sflags"; 
			shift;;
		\-o)
			echo oarg is "'"$2"'"; oarg="$2"; shift;
			shift;;
		\-\-)
			shift; break;;
	esac
done
echo single-char flags: "'"$sflags"'"
echo oarg is "'"$oarg"'"
.Ed
.Pp
This code will accept any of the following as equivalent:
.Pp
.Bd -literal -offset indent
cmd \-aoarg file file
cmd \-a \-o arg file file
cmd \-oarg -a file file
cmd \-a \-oarg \-\- file file
.Pp
.Ed
.Sh SEE ALSO
.Xr sh 1 ,
.Xr getopt 3
.Sh DIAGNOSTICS
.Nm Getopt
prints an error message on the standard error output and exits with
status > 0 when it encounters an option letter not included in
.Ar optstring .
.Sh HISTORY
Written by
.An Henry Spencer ,
working from a Bell Labs manual page.
Behavior believed identical to the Bell version. Example changed in
.Fx
version 3.2 and 4.0.
.Sh BUGS
Whatever
.Xr getopt 3
has.
.Pp
Arguments containing white space or embedded shell metacharacters
generally will not survive intact;  this looks easy to fix but
isn't. People trying to fix 
.Nm getopt
or the example in this manpage should check the history of this file
in
.Fx .
.Pp
The error message for an invalid option is identified as coming
from
.Nm getopt
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
.Nm set
command to set the arguments without disrupting the value(s) of
shell options varies from one shell version to another.
.Pp
Each shellscript has to carry complex code to parse arguments halfway
correcty (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.