getopt(3C) getopt(3C)
NAME
getopt - get option letter from argument vector
SYNOPSIS
#include <unistd.h>
int getopt (int argc, char *const *argv, const char *optstring);
extern char *optarg;
extern int optind, opterr, optopt;
DESCRIPTION
getopt returns the next option letter in argv that matches a
letter in optstring. It supports all the rules of the command
syntax standard [see intro(1)]. Since all new commands are
intended to adhere to the command syntax standard, they should
use getopts(1), getopt(3C), or getsubopt(3C) to parse
positional parameters and check for options that are legal for
that command.
optstring must contain the option letters that the command
using getopt will recognize. If a letter is followed by a
colon, the option is expected to have an argument, or group of
arguments, which may be separated from it by white space.
optarg is set to point to the start of the option argument on
return from getopt.
getopt places in optind the argv index of the next argument to
be processed. optind is external and is initialized to 1
before the first call to getopt. When all options have been
processed (that is, up to the first non-option argument),
getopt returns EOF. The special option ``--'' (two hyphens)
may be used to delimit the end of the options; when it is
encountered, EOF is returned and ``--'' is skipped. This is
useful in delimiting non-option arguments that begin with
``-'' (hyphen).
Files
/usr/lib/locale/locale/LC_MESSAGES/uxlibc
language-specific message file [See LANG on environ(5).]
Errors
getopt prints an error message on the standard error and
returns a ``?'' (question mark) when it encounters an option
letter not included in optstring or no argument after an
option that expects one. This error message may be disabled
by setting opterr to 0. The message is printed in the
standard error format. The value of the character that caused
Copyright 1994 Novell, Inc. Page 1
getopt(3C) getopt(3C)
the error is in optopt.
The label defined by a call to setlabel(3C) will be used if
available; otherwise the name of the utility (argv[0]) will be
used.
USAGE
The following code fragment shows how one might process the
arguments for a command that can take the mutually exclusive
options a and b, and the option o, which requires an argument:
#include <unistd.h>
#include <stdio.h>
main (int argc, char **argv)
{
int c;
extern char *optarg;
extern int optind;
int aflg = 0;
int bflg = 0;
int errflg = 0;
char *ofile = NULL;
while ((c = getopt(argc, argv, "abo:")) != EOF)
switch (c) {
case 'a':
if (bflg)
errflg++;
else
aflg++;
break;
case 'b':
if (aflg)
errflg++;
else
bflg++;
break;
case 'o':
ofile = optarg;
(void)printf("ofile = %s\n", ofile);
break;
case '?':
errflg++;
}
if (errflg) {
(void)fprintf(stderr,
"usage: cmd [-a|-b] [-o<file>] files...\n");
Copyright 1994 Novell, Inc. Page 2
getopt(3C) getopt(3C)
exit (2);
}
for ( ; optind < argc; optind++)
(void)printf("%s\n", argv[optind]);
return 0;
}
REFERENCES
getopts(1), getsubopt(3C), intro(1), pfmt(3C), setlabel(3C)
NOTICES
The library routine getopt does not fully check for mandatory
arguments. That is, given an option string a:b and the input
-a -b, getopt assumes that -b is the mandatory argument to the
option -a and not that -a is missing a mandatory argument.
It is a violation of the command syntax standard [see
intro(1)] for options with arguments to be grouped with other
options, as in cmd -aboxxx file, where a and b are options, o
is an option that requires an argument, and xxx is the
argument to o. Although this syntax is permitted in the
current implementation, it should not be used because it may
not be supported in future releases. The correct syntax is
cmd -ab -o xxx file.
Copyright 1994 Novell, Inc. Page 3