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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)
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