NetBSD/lib/libc/stdlib/getopt.3

.\" Copyright (c) 1988, 1991 Regents of the University of California.
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     from: @(#)getopt.3	6.16 (Berkeley) 4/19/91
.\"	$Id: getopt.3,v 1.5 1993/10/13 17:23:39 jtc Exp $
.\"
.Dd April 19, 1991
.Dt GETOPT 3
.Os BSD 4.3
.Sh NAME
.Nm getopt
.Nd get option letter from argv
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fn getopt "int argc" "char * const *argv" "const char *optstring"
.Vt extern char *optarg;
.Vt extern int optind;
.Vt extern int opterr;
.Vt extern int optopt;
.Sh DESCRIPTION
The
.Fn getopt
function gets 
the next
.Em known
option character from
.Fa argv .
An option character is
.Em known
if it has been specified in the string of accepted option characters,
.Fa optstring .
.Pp
The option string
.Fa optstring
may contain the following characters; letters and
letters followed by a colon to indicate an option argument
is to follow. It does not matter to
.Fn getopt
if a following argument has leading white space.
.Pp
On return from
.Fn getopt ,
.Va optarg
points to an option argument, if it is anticipated,
and the variable
.Va optind
contains the index to the next
.Fa argv
argument for a subsequent call
to
.Fn getopt .
.Pp
The variable
.Va opterr
and
.Va optind
are both initialized to 1.
In order to use
.Fn getopt
to evaluate multiple sets of arguments, or to evaluate a single set of
arguments multiple times,
.Va optind
must be initialized to the number of argv entries to be skipped in each
evaluation.
.Pp
The
.Fn getopt
function
returns \-1
when the argument list is exhausted.
The interpretation of options in the argument list may be cancelled
by the option
.Ql --
(double dash) which causes
.Fn getopt
to signal the end of argument processing and return \-1.
When all options have been processed (i.e., up to the first non-option
argument),
.Fn getopt
returns \-1.
.Sh DIAGNOSTICS
If the 
.Fn getopt
function encounters an option character that is not contained in 
.Fa optstring ,
it returns a question mark 
.Pq ? 
character.
If it detects a missing option argument, it returns a colon 
.Pq \: 
character if the first character of
.Fa optstring 
is a colon, otherwise it returns a question mark.
In either case, a diagnostic message is written to 
.Em stderr
unless the application has set 
.Va opterr
to zero or the first character of
.Fa optstring
is a colon.
.Sh EXAMPLE
.\" The following example comes from section E.9.7 of the IEEE 1003.2-90
.\" standard (POSIX.2).
The following code fragment shows how one might process the arguments for 
a utility that can take the mutually exclusive options 
.Em a 
and 
.Em b 
and the options 
.Em f 
and 
.Em o ,
both of which require arguments:
.Pp
.Bd -literal -compact
#include <unistd.h>

int
main (argc, argv)
	int argc;
	char *argv[];
{
	int c, bflg, aflg, errflg = 0;
	char *ifile, *ofile;
	extern char *optarg;
	extern int optind, optopt;

	. . .

	while ((c = getopt(argc, argv, ":abf:o:")) != -1) {
		switch(ch) {
		case 'a':
			if (bflg)
				errflg = 1;
			else
				aflg = 1;
			break;
		case 'b':
			if (aflg)
				errflg = 1;
			else
				bflg = 1;
			break;
		case 'f':
			ifile = optarg;
			break;
		case 'o':
			ofile = optarg;
			break;
		case ':':	/* -f or -o without option-arg */
			fprintf (stderr,
				"Option -%c requires an option-argument\\n",
				optopt);
			errflg = 1;
			break;
		case '?':
			fprintf (stderr,
				"Unrecognized option: -%c\\n",
				optopt);
			errflg = 1;
			break;
		}
	}

	if (errflg) {
		fprintf (stderr, "usage: . . .\\n");
		exit (2);
	}

	argc -= optind;
	argv += optind;

	. . .

}
.Ed
.Sh STANDARDS
The
.Fn getopt
function conforms to
.St -p1003.2-92 .
.Sh HISTORY
The
.Fn getopt
function appeared
.Bx 4.3 .
.Sh BUGS
The
.Fn getopt
function was once specified to return
.Dv EOF 
instead of \-1.
This was changed by
.St -p1003.2-92
to decouple 
.Fn getopt
from 
.Pa <stdio.h> .
.Pp
Option arguments are allowed to begin with
.Dq Li \- ;
this is reasonable but
reduces the amount of error checking possible.
.Pp
A single dash
.Dq Li -
may be specified as an character in
.Fa optstring ,
however it should
.Em never
have an argument associated with it.
This allows
.Fn getopt
to be used with programs that expect
.Dq Li -
as an option flag.
This practice is wrong, and should not be used in any current development.
It is provided for backward compatibility
.Em only .
By default, a single dash causes
.Fn getopt
to returns \-1.
This is, we believe, compatible with System V.
.Pp
It is also possible to handle digits as option letters.
This allows
.Fn getopt
to be used with programs that expect a number
.Pq Dq Li \&-\&3
as an option.
This practice is wrong, and should not be used in any current development.
It is provided for backward compatibility
.Em only .
The following code fragment works fairly well.
.Bd -literal -offset indent
int length;
char *p;

while ((c = getopt(argc, argv, "0123456789")) != -1)
	switch (c) {
	case '0': case '1': case '2': case '3': case '4':
	case '5': case '6': case '7': case '8': case '9':
		p = argv[optind - 1];
		if (p[0] == '-' && p[1] == ch && !p[2])
			length = atoi(++p);
		else
			length = atoi(argv[optind] + 1);
		break;
	}
}
.Ed