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GETOPT(3)			    Linux Programmer's Manual				GETOPT(3)

       getopt - Parse command line options

       #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);

       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 ele-
       ment.  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 exter-
       nal  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,  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  pro-
       cessing	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

       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 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 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.

       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 non-option argument is

	      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.

       The following example program illustrates the use of getopt_long() with most of	its  fea-

       #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);

       The POSIX.2 specification of getopt() has a technical error described in POSIX.2 Interpre-
       tation 150.  The GNU implementation (and probably all  other  implementations)  implements
       the correct behaviour rather than that specified.

	      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					    2002-02-16					GETOPT(3)
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