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+.\" Copyright (c) 1988, 1991, 1993
+.\"     The 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.
+.\"
+.\"     $OpenBSD: getopt.3,v 1.17 2002/08/19 22:29:52 miod Exp $
+.\"
+.Dd April 19, 1994
+.Dt GETOPT 3
+.Os
+.Sh NAME
+.Nm getopt
+.Nd get option character from command line argument list
+.Sh SYNOPSIS
+.Fd #include <unistd.h>
+.Vt extern char *optarg;
+.Vt extern int   optind;
+.Vt extern int   optopt;
+.Vt extern int   opterr;
+.Vt extern int   optreset;
+.Ft int
+.Fn getopt "int argc" "char * const *argv" "const char *optstring"
+.Sh DESCRIPTION
+The
+.Fn getopt
+function incrementally parses a command line argument list
+.Fa argv
+and returns the next known option character.
+An option character is
+.Dq 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 elements: individual characters and
+characters followed by a colon to indicate an option argument
+is to follow.
+For example, an option string
+.Qq x
+recognizes an option
+.Fl x ,
+and an option string
+.Qq Li x:
+recognizes an option and argument
+.Fl x Ar argument .
+It does not matter to
+.Fn getopt
+if a following argument has leading whitespace.
+.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 .
+The variable
+.Va optopt
+saves the last known option character returned by
+.Fn getopt .
+.Pp
+The variables
+.Va opterr
+and
+.Va optind
+are both initialized to 1.
+The
+.Va optind
+variable may be set to another value before a set of calls to
+.Fn getopt
+in order to skip over more or less argv entries.
+.Pp
+In order to use
+.Fn getopt
+to evaluate multiple sets of arguments, or to evaluate a single set of
+arguments multiple times,
+the variable
+.Va optreset
+must be set to 1 before the second and each additional set of calls to
+.Fn getopt ,
+and the variable
+.Va optind
+must be reinitialized.
+.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 returns \-1.
+When all options have been processed (i.e., up to the first non-option
+argument),
+.Fn getopt
+returns \-1.
+.Sh EXAMPLES
+.Bd -literal -compact
+int bflag, ch, fd;
+
+bflag = 0;
+while ((ch = getopt(argc, argv, "bf:")) != -1) {
+        switch (ch) {
+        case 'b':
+                bflag = 1;
+                break;
+        case 'f':
+                if ((fd = open(optarg, O_RDONLY, 0)) < 0) {
+                        (void)fprintf(stderr,
+                            "myname: %s: %s\en", optarg, strerror(errno));
+                        exit(1);
+                }
+                break;
+        case '?':
+        default:
+                usage();
+        }
+}
+argc -= optind;
+argv += optind;
+.Ed
+.Sh SEE ALSO
+.Xr getopt 1 ,
+.Xr getsubopt 3
+.Sh DIAGNOSTICS
+If the
+.Fn getopt
+function encounters a character not found in the string
+.Va optstring
+or detects
+a missing option argument it writes an error message to
+.Em stderr
+and returns
+.Ql ? .
+Setting
+.Va opterr
+to a zero will disable these error messages.
+If
+.Va optstring
+has a leading
+.Ql \&:
+then a missing option argument causes a
+.Ql \&:
+to be returned in addition to suppressing any error messages.
+.Pp
+Option arguments are allowed to begin with
+.Ql - ;
+this is reasonable but reduces the amount of error checking possible.
+.Sh EXTENSIONS
+The
+.Va optreset
+variable was added to make it possible to call the
+.Fn getopt
+function multiple times.
+This is an extension to the
+.St -p1003.2
+specification.
+.Sh HISTORY
+The
+.Fn getopt
+function appeared in
+.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
+A single dash
+.Pq Ql -
+may be specified as a 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
+.Ql -
+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 return \-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 in most cases.
+.Bd -literal -offset indent
+long 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 = ch - '0';
+                else
+                        length = strtol(argv[optind] + 1, NULL, 10);
+                break;
+        }
+}
+.Ed