Add getopt_long library function
This commit is contained in:
Erik van der Kouwe
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.\" $NetBSD: getopt_long.3,v 1.18 2007/07/02 17:56:17 ginsbach 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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.\" 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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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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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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.\"
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.Dd July 2, 2007
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.Dt GETOPT_LONG 3
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.Os
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.Sh NAME
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.Nm getopt_long
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.Nd get long options 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 getopt.h
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.Ft int
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.Fn getopt_long "int argc" "char * const *argv" "const char *optstring" "struct option *long_options" "int *index"
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.Sh DESCRIPTION
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The
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.Fn getopt_long
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function is similar to
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.Xr getopt 3
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but it accepts options in two forms: words and characters.
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The
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.Fn getopt_long
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function provides a superset of the functionality of
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.Xr getopt 3 .
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.Fn getopt_long
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can be used in two ways.
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In the first way, every long option understood by the program has a
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corresponding short option, and the option structure is only used to
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translate from long options to short options.
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When used in this fashion,
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.Fn getopt_long
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behaves identically to
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.Xr getopt 3 .
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This is a good way to add long option processing to an existing program
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with the minimum of rewriting.
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.Pp
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In the second mechanism, a long option sets a flag in the
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.Fa option
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structure passed, or will store a pointer to the command line argument
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in the
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.Fa option
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structure passed to it for options that take arguments.
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Additionally, the long option's argument may be specified as a single
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argument with an equal sign, e.g.
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.Bd -literal
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myprogram --myoption=somevalue
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.Ed
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.Pp
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When a long option is processed the call to
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.Fn getopt_long
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will return 0.
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For this reason, long option processing without
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shortcuts is not backwards compatible with
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.Xr getopt 3 .
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.Pp
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It is possible to combine these methods, providing for long options
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processing with short option equivalents for some options.
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Less frequently used options would be processed as long options only.
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.Pp
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Abbreviated long option names are accepted when
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.Fn getopt_long
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processes long options if the abbreviation is unique.
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An exact match is always preferred for a defined long option.
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.Pp
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The
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.Fn getopt_long
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call requires a structure to be initialized describing the long options.
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The structure is:
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.Bd -literal
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struct option {
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char *name;
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int has_arg;
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int *flag;
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int val;
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};
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.Ed
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.Pp
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The
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.Fa name
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field should contain the option name without the leading double dash.
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.Pp
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The
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.Fa has_arg
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field should be one of:
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.Bl -tag -width "optional_argument"
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.It Li no_argument
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no argument to the option is expect.
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.It Li required_argument
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an argument to the option is required.
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.It Li optional_argument
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an argument to the option may be presented.
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.El
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.Pp
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If
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.Fa flag
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is not
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.Dv NULL ,
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then the integer pointed to by it will be set to the value in the
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.Fa val
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field.
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If the
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.Fa flag
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field is
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.Dv NULL ,
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then the
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.Fa val
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field will be returned.
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Setting
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.Fa flag
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to
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.Dv NULL
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and setting
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.Fa val
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to the corresponding short option will make this function act just
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like
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.Xr getopt 3 .
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.Pp
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If the
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.Fa index
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field is not
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.Dv NULL ,
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the integer it points to will be set to the index of the long option
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in the
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.Fa long_options
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array.
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.Pp
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The last element of the
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.Fa long_options
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array has to be filled with zeroes (see
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.Sx EXAMPLES
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section).
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.Sh EXAMPLES
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.Bd -literal -compact
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extern char *optarg;
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extern int optind;
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int bflag, ch, fd;
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int daggerset;
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/* options descriptor */
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static struct option longopts[] = {
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{ "buffy", no_argument, 0, 'b' },
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{ "fluoride", required_argument, 0, 'f' },
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{ "daggerset", no_argument, \*[Am]daggerset, 1 },
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{ NULL, 0, NULL, 0 }
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};
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bflag = 0;
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while ((ch = getopt_long(argc, argv, "bf:", longopts, NULL)) != -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 0:
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if(daggerset) {
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fprintf(stderr,"Buffy will use her dagger to "
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"apply fluoride to dracula's teeth\en");
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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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argc -= optind;
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argv += optind;
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.Ed
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.Sh IMPLEMENTATION DIFFERENCES
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This section describes differences to the GNU implementation
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found in glibc-2.1.3:
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.Bl -tag -width "xxx"
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.It Li o
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handling of - as first char of option string in presence of
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environment variable POSIXLY_CORRECT:
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.Bl -tag -width "NetBSD"
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.It Li GNU
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ignores POSIXLY_CORRECT and returns non-options as
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arguments to option '\e1'.
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.It Li NetBSD
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honors POSIXLY_CORRECT and stops at the first non-option.
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.El
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.It Li o
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handling of :: in options string in presence of POSIXLY_CORRECT:
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.Bl -tag -width "NetBSD"
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.It Li Both
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GNU and NetBSD ignore POSIXLY_CORRECT here and take :: to
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mean the preceding option takes an optional argument.
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.El
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.It Li o
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return value in case of missing argument if first character
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(after + or -) in option string is not ':':
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.Bl -tag -width "NetBSD"
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.It Li GNU
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returns '?'
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.It NetBSD
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returns ':' (since NetBSD's getopt does).
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.El
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.It Li o
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handling of --a in getopt:
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.Bl -tag -width "NetBSD"
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.It Li GNU
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parses this as option '-', option 'a'.
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.It Li NetBSD
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parses this as '--', and returns \-1 (ignoring the a).
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(Because the original getopt does.)
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.El
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.It Li o
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setting of optopt for long options with flag !=
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.Dv NULL :
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.Bl -tag -width "NetBSD"
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.It Li GNU
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sets optopt to val.
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.It Li NetBSD
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sets optopt to 0 (since val would never be returned).
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.El
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.It Li o
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handling of -W with W; in option string in getopt (not getopt_long):
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.Bl -tag -width "NetBSD"
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.It Li GNU
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causes a segfault.
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.It Li NetBSD
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returns \-1, with optind pointing past the argument of -W
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(as if `-W arg' were `--arg', and thus '--' had been found).
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.\" How should we treat W; in the option string when called via
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.\" getopt? Ignore the ';' or treat it as a ':'? Issue a warning?
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.El
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.It Li o
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setting of optarg for long options without an argument that are
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invoked via -W (W; in option string):
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.Bl -tag -width "NetBSD"
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.It Li GNU
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sets optarg to the option name (the argument of -W).
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.It Li NetBSD
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sets optarg to
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.Dv NULL
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(the argument of the long option).
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.El
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.It Li o
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handling of -W with an argument that is not (a prefix to) a known
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long option (W; in option string):
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.Bl -tag -width "NetBSD"
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.It Li GNU
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returns -W with optarg set to the unknown option.
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.It Li NetBSD
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treats this as an error (unknown option) and returns '?' with
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optopt set to 0 and optarg set to
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.Dv NULL
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(as GNU's man page documents).
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.El
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.It Li o
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The error messages are different.
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.It Li o
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NetBSD does not permute the argument vector at the same points in
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the calling sequence as GNU does.
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The aspects normally used by the caller
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(ordering after \-1 is returned, value of optind relative
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to current positions) are the same, though.
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(We do fewer variable swaps.)
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.El
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.Sh SEE ALSO
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.Xr getopt 3
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.Sh HISTORY
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The
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.Fn getopt_long
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function first appeared in GNU libiberty.
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The first
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.Nx
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implementation appeared in 1.5.
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.Sh BUGS
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The implementation can completely replace
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.Xr getopt 3 ,
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but right now we are using separate code.
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.Pp
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The
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.Fa argv
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argument is not really const.
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