Name

getopt, getopt_long, getopt_long_only — 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 characters of this element (aside from the initial '−') are option characters. 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 argument, 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 (i.e., in the same word as the option name itself, for example, "−oarg"), then it is returned in optarg, otherwise optarg is set to zero. This is a GNU extension. If optstring contains W followed 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 behavior is a GNU extension, not available with libraries before glibc 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 nonzero (which is the default), getopt() prints an error message.

The getopt_long() function works like getopt() except that it also accepts long options, started with 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 argument.

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 character.) 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 character 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 parameter.

ENVIRONMENT

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(1) 2.0 to communicate to glibc which arguments are the results of wildcard expansion and so should not be considered as options. This behavior was removed in bash(1) version 2.01, but the support remains in glibc.

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>

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 behavior rather than that specified.

EXAMPLE

The following trivial example program uses getopt() to handle two program options: −n, with no associated value; and −t val, which expects an associated value.

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>

int
main(int argc, char *argv[])
{
    int flags, opt;
    int nsecs, tfnd;

    nsecs = 0;
    tfnd = 0;
    flags = 0;
    while ((opt = getopt(argc, argv, "nt:")) != −1) {
        switch (opt) {
        case 'n':
            flags = 1;
            break;
        case 't':
            nsecs = atoi(optarg);
            tfnd = 1;
            break;
        default: /* '?' */
            fprintf(stderr, "Usage: %s [−t nsecs] [−n] name\n",
                    argv[0]);
            exit(EXIT_FAILURE);
        }
    }

    printf("flags=%d; tfnd=%d; optind=%d\n", flags, tfnd, optind);

    if (optind >= argc) {
        fprintf(stderr, "Expected argument after options\n");
        exit(EXIT_FAILURE);
    }

    printf("name argument = %s\n", argv[optind]);

    /* Other code omitted */

    exit(EXIT_SUCCESS);
}

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(EXIT_SUCCESS);
}

SEE ALSO

getsubopt(3), feature_test_macros(7)

COLOPHON

This page is part of release 2.79 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


  (c) 1993 by Thomas Koenig (ig25rz.uni-karlsruhe.de)

Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

Since the Linux kernel and libraries are constantly changing, this
manual page may be incorrect or out-of-date.  The author(s) assume no
responsibility for errors or omissions, or for damages resulting from
the use of the information contained herein.  The author(s) may not
have taken the same level of care in the production of this manual,
which is licensed free of charge, as they might when working
professionally.

Formatted or processed versions of this manual, if unaccompanied by
the source, must acknowledge the copyright and authors of this work.
License.
Modified Sat Jul 24 19:27:50 1993 by Rik Faith (faithcs.unc.edu)
Modified Mon Aug 30 22:02:34 1995 by Jim Van Zandt <jrvvanzandt.mv.com>
 longindex is a pointer, has_arg can take 3 values, using consistent
 names for optstring and longindex, "\n" in formats fixed.  Documenting
 opterr and getopt_long_only.  Clarified explanations (borrowing heavily
 from the source code).
Modified 8 May 1998 by Joseph S. Myers (jsm28cam.ac.uk)
Modified 990715, aeb: changed `EOF' into `-1' since that is what POSIX
 says; moreover, EOF is not defined in <unistd.h>.
Modified 2002-02-16, joey: added information about non-existing
 option character and colon as first option character
Modified 2004-07-28, Michael Kerrisk <mtk.manpagesgmail.com>
Added text to explain how to order both '[-+]' and ':' at
the start of optstring
Modified 2006-12-15, mtk, Added getopt() example program.