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

     #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 characters of this  ele-
     ment (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

     If there are no more  option  characters,  getopt()  returns
     EOF.   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 char-
     acters.   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 opt-
     string 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 char-
     acter 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 writ-
     ten  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.

     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


     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 EOF 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 EOF 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 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, from the source code,  illus-
     trates the use of getopt_long() with most of its features.

     #include <stdio.h>

     main (argc, argv)
          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);


     This manpage is confusing.

     The POSIX.2 specification of getopt() has a technical  error
     described  in POSIX.2 Interpretation 150.  The GNU implemen-
     tation (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.