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 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

       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

       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

       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 argu-

       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

       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-


              If  this  is set, then option processing stops as soon as a non-
              option 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.


       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 '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  Interpretation  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 proto-
              type to be compatible with other systems.

GNU                               2002-02-16                         getopt(3)