*nix Documentation Project
·  Home
 +   man pages
·  Linux HOWTOs
·  FreeBSD Tips
·  *niX Forums

  man pages->Linux man pages -> getopt (3)              



NAME    [Toc]    [Back]

       getopt - Parse command line options

SYNOPSIS    [Toc]    [Back]

       #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    [Toc]    [Back]

       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

       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, 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  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

       The  getopt_long()  function  works  like  getopt() except that it also
       accepts long options, started out by two dashes.  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.

	      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    [Toc]    [Back]

       The  getopt()  function	returns the option character if the option was
       found successfully, `:' if there was a missing parameter for one of the
       options,  `?' for an unknown option character, or -1 for the end of the
       option list.

       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.


	      If this is set, then option processing stops as soon as  a  nonoption
 argument is encountered.

	      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    [Toc]    [Back]

       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>

       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)

	       switch (c) {
	       case 0:
		   printf ("option %s", long_options[option_index].name);
		   if (optarg)
		       printf (" with arg %s", optarg);
		   printf ("\n");

	       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);

	       case 'a':
		   printf ("option a\n");

	       case 'b':
		   printf ("option b\n");

	       case 'c':
		   printf ("option c with value `%s'\n", optarg);

	       case 'd':
		   printf ("option d with value `%s'\n", optarg);

	       case '?':

		   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    [Toc]    [Back]

       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    [Toc]    [Back]

	      POSIX.2, 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.

GNU				  1998-05-08			     GETOPT(3)
[ Back ]
 Similar pages
Name OS Title
getopt FreeBSD parse command options
getopt OpenBSD parse command options
getopt HP-UX parse command options
getopt IRIX parse command options
getopts IRIX parse command options
getopt Linux parse command options (enhanced)
getopts HP-UX parse utility (command) options
getsubopt Tru64 Parse suboption arguments from a command line
parseargv IRIX process command-line options
Getopt::Long IRIX extended processing of command line options
Copyright © 2004-2005 DeniX Solutions SRL
newsletter delivery service