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getopt.1 revision 1.7 
 $NetBSD: getopt.1,v 1.7 1997/07/18 00:18:26 phil Exp $
.Dd June 21, 1993
.Dt GETOPT 1
.Os
.Sh NAME
.Nm getopt
.Nd parse command options
.Sh SYNOPSIS
.Nm args=\`getopt optstring $*\`
.Nm set -- \`getopt optstring $*\`
.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.
.Op 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
.Dq --
is used to delimit the end of the options.
.Nm Getopt
will place
.Dq --
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
.Dq -
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
.Op a
and
.Op b ,
and the option
.Op o ,
which requires an argument.

p
d -literal -offset indent args=\`getopt abo: $*\`
if test $? != 0
then
 echo 'Usage: ...'
 exit 2
fi
set -- $args
for i
do
 case "$i"
 in
 -a|-b)
 flag=$i; shift;;
 -o)
 oarg=$2; shift; shift;;
 --)
 shift; break;;
 esac
done
.Ed

p
This code will accept any of the following as equivalent:

p
d -literal -offset indent cmd -aoarg file file
cmd -a -o arg file file
cmd -oarg -a file file
cmd -a -oarg -- file file
.Ed

p
.St -p1003.2
mandates that the 
.Nm sh
set command return the value of 0 for the exit status. Therefore,
the exit status of the
.Nm getopt
command is lost when
.Nm getopt
and the
.Nm sh
set command are used on the same line. The example given
is one way to detect errors found by 
.Nm getopt .
.Sh SEE ALSO
.Xr sh 1 ,
.Xr getopt 3
.Sh DIAGNOSTICS
.Nm Getopt
prints an error message on the standard error output when it
encounters an option letter not included in
.Op optstring .
.Sh HISTORY
Written by Henry Spencer, working from a Bell Labs manual page.
Behavior believed identical to the Bell version.
.Sh BUGS
Whatever
.Xr getopt 3
has.

p
Arguments containing white space or embedded shell metacharacters
generally will not survive intact; this looks easy to fix but isn't.

p
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.

p
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.