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GETOPT(3) Linux Programmer's Manual GETOPT(3)
NAME
getopt - Parse command-line options
SYNOPSIS
#include <unistd.h>
int getopt(int argc, char * const argv[],
const char *optstring);
extern char *optarg;
extern int optind, opterr, optopt;
#define _GNU_SOURCE
#include <getopt.h>
int getopt_long(int argc, char * const argv[],
const char *optstring,
const struct option *longopts, int *longindex);
int getopt_long_only(int argc, char * const argv[],
const char *optstring,
const struct option *longopts, int *longindex);
DESCRIPTION
The getopt() function parses the command-line arguments. Its arguments
argc and argv are the argument count and array as passed to the main()
function on program invocation. An element of argv that starts with
'-' (and is not exactly "-" or "--") is an option element. The charac-
ters of this element (aside from the initial '-') are option charac-
ters. If getopt() is called repeatedly, it returns successively each
of the option characters from each of the option elements.
If getopt() finds another option character, it returns that character,
updating the external variable optind and a static variable nextchar so
that the next call to getopt() can resume the scan with the following
option character or argv-element.
If there are no more option characters, getopt() returns -1. Then
optind is the index in argv of the first argv-element that is not an
option.
optstring is a string containing the legitimate option characters. If
such a character is followed by a colon, the option requires an argu-
ment, so getopt() places a pointer to the following text in the same
argv-element, or the text of the following argv-element, in optarg.
Two colons mean an option takes an optional arg; if there is text in
the current argv-element, it is returned in optarg, otherwise optarg is
set to zero. This is a GNU extension. If optstring contains W fol-
lowed by a semicolon, then -W foo is treated as the long option --foo.
(The -W option is reserved by POSIX.2 for implementation extensions.)
This behaviour is a GNU extension, not available with libraries before
GNU libc 2.
By default, getopt() permutes the contents of argv as it scans, so that
eventually all the non-options are at the end. Two other modes are
also implemented. If the first character of optstring is '+' or the
environment variable POSIXLY_CORRECT is set, then option processing
stops as soon as a non-option argument is encountered. If the first
character of optstring is '-', then each non-option argv-element is
handled as if it were the argument of an option with character code 1.
(This is used by programs that were written to expect options and other
argv-elements in any order and that care about the ordering of the
two.) The special argument "--" forces an end of option-scanning
regardless of the scanning mode.
If getopt() does not recognize an option character, it prints an error
message to stderr, stores the character in optopt, and returns '?'.
The calling program may prevent the error message by setting opterr to
0.
If getopt() finds an option character in argv that was not included in
optstring, or if it detects a missing option argument, it returns '?'
and sets the external variable optopt to the actual option character.
If the first character (following any optional '+' or '-' described
above) of optstring is a colon (':'), then getopt() returns ':' instead
of '?' to indicate a missing option argument. If an error was
detected, and the first character of optstring is not a colon, and the
external variable opterr is non-zero (which is the default), getopt()
prints an error message.
The getopt_long() function works like getopt() except that it also
accepts long options, started out by two dashes. (If the program
accepts only long options, then optstring should be specified as an
empty string (""), not NULL.) Long option names may be abbreviated if
the abbreviation is unique or is an exact match for some defined
option. A long option may take a parameter, of the form --arg=param or
--arg param.
longopts is a pointer to the first element of an array of struct option
declared in <getopt.h> as
struct option {
const char *name;
int has_arg;
int *flag;
int val;
};
The meanings of the different fields are:
name is the name of the long option.
has_arg
is: no_argument (or 0) if the option does not take an argument;
required_argument (or 1) if the option requires an argument; or
optional_argument (or 2) if the option takes an optional argu-
ment.
flag specifies how results are returned for a long option. If flag
is NULL, then getopt_long() returns val. (For example, the
calling program may set val to the equivalent short option char-
acter.) Otherwise, getopt_long() returns 0, and flag points to
a variable which is set to val if the option is found, but left
unchanged if the option is not found.
val is the value to return, or to load into the variable pointed to
by flag.
The last element of the array has to be filled with zeroes.
If longindex is not NULL, it points to a variable which is set to the
index of the long option relative to longopts.
getopt_long_only() is like getopt_long(), but '-' as well as '--' can
indicate a long option. If an option that starts with '-' (not '--')
doesn't match a long option, but does match a short option, it is
parsed as a short option instead.
RETURN VALUE
If an option was successfully found, then getopt() returns the option
character. If all command-line options have been parsed, then getopt()
returns -1. If getopt() encounters an option character that was not in
optstring, then '?' is returned. If getopt() encounters an option with
a missing argument, then the return value depends on the first charac-
ter in optstring: if it is ':', then ':' is returned; otherwise '?' is
returned.
getopt_long() and getopt_long_only() also return the option character
when a short option is recognized. For a long option, they return val
if flag is NULL, and 0 otherwise. Error and -1 returns are the same as
for getopt(), plus '?' for an ambiguous match or an extraneous parame-
ter.
ENVIRONMENT VARIABLES
POSIXLY_CORRECT
If this is set, then option processing stops as soon as a non-
option argument is encountered.
_<PID>_GNU_nonoption_argv_flags_
This variable was used by bash 2.0 to communicate to GNU libc
which arguments are the results of wildcard expansion and so
should not be considered as options. This behaviour was removed
in bash version 2.01, but the support remains in GNU libc.
EXAMPLE
The following example program illustrates the use of getopt_long() with
most of its features.
#include <stdio.h> /* for printf */
#include <stdlib.h> /* for exit */
#include <getopt.h>
int
main (int argc, char **argv) {
int c;
int digit_optind = 0;
while (1) {
int this_option_optind = optind ? optind : 1;
int option_index = 0;
static struct option long_options[] = {
{"add", 1, 0, 0},
{"append", 0, 0, 0},
{"delete", 1, 0, 0},
{"verbose", 0, 0, 0},
{"create", 1, 0, 'c'},
{"file", 1, 0, 0},
{0, 0, 0, 0}
};
c = getopt_long (argc, argv, "abc:d:012",
long_options, &option_index);
if (c == -1)
break;
switch (c) {
case 0:
printf ("option %s", long_options[option_index].name);
if (optarg)
printf (" with arg %s", optarg);
printf ("\n");
break;
case '0':
case '1':
case '2':
if (digit_optind != 0 && digit_optind != this_option_optind)
printf ("digits occur in two different argv-elements.\n");
digit_optind = this_option_optind;
printf ("option %c\n", c);
break;
case 'a':
printf ("option a\n");
break;
case 'b':
printf ("option b\n");
break;
case 'c':
printf ("option c with value '%s'\n", optarg);
break;
case 'd':
printf ("option d with value '%s'\n", optarg);
break;
case '?':
break;
default:
printf ("?? getopt returned character code 0%o ??\n", c);
}
}
if (optind < argc) {
printf ("non-option ARGV-elements: ");
while (optind < argc)
printf ("%s ", argv[optind++]);
printf ("\n");
}
exit (0);
}
BUGS
The POSIX.2 specification of getopt() has a technical error described
in POSIX.2 Interpretation 150. The GNU implementation (and probably
all other implementations) implements the correct behaviour rather than
that specified.
CONFORMING TO
getopt():
POSIX.2 and POSIX.1-2001, provided the environment variable
POSIXLY_CORRECT is set. Otherwise, the elements of argv aren't
really const, because we permute them. We pretend they're const
in the prototype to be compatible with other systems.
On some older implementations, getopt() was declared in
<stdio.h>. SUSv1 permitted the declaration to appear in either
<unistd.h> or <stdio.h>. POSIX.1-2001 marked the use of
<stdio.h> for this purpose as LEGACY. POSIX.1-2001 does not
allow the declaration to appear in <stdio.h>.
GNU 2004-07-28 GETOPT(3)
Man(1) output converted with
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This page was generated on Sat Sep 8 16:39:42 GMT 2007
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