364 lines
8.4 KiB
Groff
364 lines
8.4 KiB
Groff
.\" 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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.\" $OpenBSD: getopt.3,v 1.46 2016/01/04 19:43:13 tb Exp $
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.\"
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.Dd $Mdocdate: January 4 2016 $
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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 SYNOPSIS
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.In unistd.h
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.Vt extern char *optarg;
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.Vt extern int opterr;
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.Vt extern int optind;
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.Vt extern int optopt;
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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,
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characters followed by a colon, and characters followed by two colons.
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A character followed by a single colon indicates that an argument
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is to follow the option on the command line.
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Two colons indicates that the argument is optional \- this is an
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extension not covered by POSIX.
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For example, an option string
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.Qq x
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recognizes an option
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.Fl x ,
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and an option string
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.Qq Li x:
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recognizes an option and argument
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.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 whitespace; except in the case where
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the argument is optional, denoted with two colons, no leading whitespace
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is permitted.
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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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.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 larger than 0 before a set of calls to
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.Fn getopt
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in order to skip over more or less
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.Fa argv
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entries.
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An
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.Va optind
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value of 0 is reserved for compatibility with GNU
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.Fn getopt .
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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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.Sq \&?
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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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.Sq \&:
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then a missing option argument causes
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.Sq \&:
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to be returned instead of
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.Sq \&? .
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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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The following code accepts the options
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.Fl b
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and
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.Fl f Ar argument
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and adjusts
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.Va argc
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and
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.Va argv
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after option argument processing has completed.
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.Bd -literal -offset indent
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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)) == -1)
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err(1, "%s", optarg);
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break;
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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
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.Em 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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.Ql - ;
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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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.Fn getopt
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function implements a superset of the functionality specified by
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.St -p1003.1 .
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.Pp
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The following extensions are supported:
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.Bl -bullet
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.It
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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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.It
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If the
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.Va optind
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variable is set to 0,
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.Fn getopt
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will behave as if the
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.Va optreset
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variable has been set.
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This is for compatibility with
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.Tn GNU
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.Fn getopt .
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New code should use
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.Va optreset
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instead.
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.It
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If the first character of
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.Fa optstring
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is a plus sign
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.Pq Ql + ,
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it will be ignored.
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This is for compatibility with
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.Tn GNU
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.Fn getopt .
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.It
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If the first character of
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.Fa optstring
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is a dash
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.Pq Ql - ,
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non-options will be returned as arguments to the option character
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.Ql \e1 .
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This is for compatibility with
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.Tn GNU
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.Fn getopt .
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.It
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A single dash
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.Pq Ql -
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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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.Ql -
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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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semantics (see above).
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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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.El
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.Pp
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Historic
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.Bx
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versions of
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.Fn getopt
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set
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.Fa optopt
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to the last option character processed.
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However, this conflicts with
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.St -p1003.1
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which stipulates that
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.Fa optopt
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be set to the last character that caused an error.
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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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It is 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 and can handle mixed
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number and letter arguments.
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.Bd -literal -offset indent
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int aflag = 0, bflag = 0, ch, lastch = '\e0';
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int length = -1, newarg = 1, prevoptind = 1;
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while ((ch = getopt(argc, argv, "0123456789ab")) != -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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if (newarg || !isdigit(lastch))
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length = 0;
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else if (length > INT_MAX / 10)
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usage();
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length = (length * 10) + (ch - '0');
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break;
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case 'a':
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aflag = 1;
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break;
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case 'b':
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bflag = 1;
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break;
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default:
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usage();
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}
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lastch = ch;
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newarg = optind != prevoptind;
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prevoptind = optind;
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}
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.Ed
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