318 lines
7.6 KiB
Groff
318 lines
7.6 KiB
Groff
.\" $NetBSD: getopt.3,v 1.34 2014/06/05 22:09:50 wiz Exp $
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.\"
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.\" Copyright (c) 1988, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)getopt.3 8.5 (Berkeley) 4/27/95
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.\" $FreeBSD$
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.\"
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.Dd June 5, 2014
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.Dt GETOPT 3
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.Os
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.Sh NAME
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.Nm getopt
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.Nd get option character from command line argument list
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In unistd.h
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.Vt extern char *optarg ;
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.Vt extern int optind ;
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.Vt extern int optopt ;
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.Vt extern int opterr ;
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.Vt extern int optreset ;
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.Ft int
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.Fn getopt "int argc" "char * const argv[]" "const char *optstring"
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.Sh DESCRIPTION
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The
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.Fn getopt
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function incrementally parses a command line argument list
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.Fa argv
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and returns the next
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.Em known
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option character.
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An option character is
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.Em known
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if it has been specified in the string of accepted option characters,
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.Fa optstring .
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.Pp
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The option string
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.Fa optstring
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may contain the following elements: individual characters, and
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characters followed by a colon to indicate an option argument
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is to follow.
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If an individual character is followed by two colons, then the
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option argument is optional;
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.Va optarg
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is set to the rest of the current
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.Va argv
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word, or
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.Dv NULL
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if there were no more characters in the current word.
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This is a
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.Tn GNU
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extension.
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For example, an option string
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.Li \&"x"
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recognizes an option
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.Dq Fl x ,
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and an option string
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.Li \&"x:"
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recognizes an option and argument
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.Dq Fl x Ar argument .
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It does not matter to
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.Fn getopt
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if a following argument has leading white space.
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.Pp
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On return from
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.Fn getopt ,
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.Va optarg
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points to an option argument, if it is anticipated,
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and the variable
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.Va optind
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contains the index to the next
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.Fa argv
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argument for a subsequent call
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to
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.Fn getopt .
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The variable
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.Va optopt
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saves the last
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.Em known
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option character returned by
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.Fn getopt .
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.Pp
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The variables
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.Va opterr
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and
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.Va optind
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are both initialized to 1.
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The
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.Va optind
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variable may be set to another value before a set of calls to
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.Fn getopt
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in order to skip over more or less argv entries.
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.Pp
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In order to use
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.Fn getopt
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to evaluate multiple sets of arguments, or to evaluate a single set of
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arguments multiple times,
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the variable
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.Va optreset
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must be set to 1 before the second and each additional set of calls to
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.Fn getopt ,
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and the variable
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.Va optind
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must be reinitialized.
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.Pp
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The
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.Fn getopt
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function returns \-1 when the argument list is exhausted.
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The interpretation of options in the argument list may be cancelled
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by the option
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.Ql --
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(double dash) which causes
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.Fn getopt
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to signal the end of argument processing and return \-1.
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When all options have been processed (i.e., up to the first non-option
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argument),
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.Fn getopt
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returns \-1.
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.Sh RETURN VALUES
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The
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.Fn getopt
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function returns the next known option character in
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.Fa optstring .
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If
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.Fn getopt
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encounters a character not found in
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.Fa optstring
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or if it detects a missing option argument,
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it returns
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.Ql \&?
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(question mark).
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If
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.Fa optstring
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has a leading
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.Ql \&:
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then a missing option argument causes
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.Ql \&:
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to be returned instead of
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.Ql \&? .
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In either case, the variable
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.Va optopt
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is set to the character that caused the error.
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The
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.Fn getopt
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function returns \-1 when the argument list is exhausted.
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.Sh EXAMPLES
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.Bd -literal -compact
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#include <unistd.h>
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int bflag, ch, fd;
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bflag = 0;
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while ((ch = getopt(argc, argv, "bf:")) != -1) {
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switch (ch) {
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case 'b':
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bflag = 1;
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break;
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case 'f':
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if ((fd = open(optarg, O_RDONLY, 0)) \*[Lt] 0) {
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(void)fprintf(stderr,
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"myname: %s: %s\en", optarg, strerror(errno));
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exit(1);
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}
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break;
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case '?':
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default:
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usage();
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}
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}
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argc -= optind;
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argv += optind;
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.Ed
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.Sh DIAGNOSTICS
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If the
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.Fn getopt
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function encounters a character not found in the string
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.Fa optstring
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or detects
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a missing option argument it writes an error message to the
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.Dv stderr
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and returns
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.Ql \&? .
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Setting
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.Va opterr
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to a zero will disable these error messages.
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If
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.Fa optstring
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has a leading
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.Ql \&:
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then a missing option argument causes a
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.Ql \&:
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to be returned in addition to suppressing any error messages.
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.Pp
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Option arguments are allowed to begin with
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.Dq Li \- ;
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this is reasonable but reduces the amount of error checking possible.
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.Sh SEE ALSO
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.Xr getopt 1 ,
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.Xr getopt_long 3 ,
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.Xr getsubopt 3
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.Sh STANDARDS
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The
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.Va optreset
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variable was added to make it possible to call the
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.Fn getopt
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function multiple times.
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This is an extension to the
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.St -p1003.2
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specification.
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.Sh HISTORY
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The
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.Fn getopt
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function appeared in
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.Bx 4.3 .
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.Sh BUGS
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The
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.Fn getopt
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function was once specified to return
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.Dv EOF
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instead of \-1.
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This was changed by
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.St -p1003.2-92
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to decouple
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.Fn getopt
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from
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.In stdio.h .
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.Pp
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A single dash
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.Dq Li -
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may be specified as a character in
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.Fa optstring ,
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however it should
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.Em never
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have an argument associated with it.
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This allows
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.Fn getopt
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to be used with programs that expect
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.Dq Li -
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as an option flag.
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This practice is wrong, and should not be used in any current development.
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It is provided for backward compatibility
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.Em only .
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Care should be taken not to use
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.Ql \&-
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as the first character in
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.Fa optstring
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to avoid a semantic conflict with
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.Tn GNU
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.Fn getopt ,
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which assigns different meaning to an
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.Fa optstring
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that begins with a
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.Ql \&- .
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By default, a single dash causes
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.Fn getopt
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to return \-1.
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.Pp
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It is also possible to handle digits as option letters.
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This allows
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.Fn getopt
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to be used with programs that expect a number
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.Pq Dq Li \&-\&3
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as an option.
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This practice is wrong, and should not be used in any current development.
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It is provided for backward compatibility
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.Em only .
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The following code fragment works in most cases.
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.Bd -literal -offset indent
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int ch;
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long length;
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char *p, *ep;
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while ((ch = getopt(argc, argv, "0123456789")) != -1)
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switch (ch) {
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case '0': case '1': case '2': case '3': case '4':
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case '5': case '6': case '7': case '8': case '9':
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p = argv[optind - 1];
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if (p[0] == '-' \*[Am]\*[Am] p[1] == ch \*[Am]\*[Am] !p[2]) {
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length = ch - '0';
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ep = "";
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} else if (argv[optind] \*[Am]\*[Am] argv[optind][1] == ch) {
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length = strtol((p = argv[optind] + 1),
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\*[Am]ep, 10);
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optind++;
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optreset = 1;
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} else
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usage();
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if (*ep != '\e0')
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errx(EX_USAGE, "illegal number -- %s", p);
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break;
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}
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.Ed
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