#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);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       getopt(): _POSIX_C_SOURCE >= 2 || _XOPEN_SOURCE
       getopt_long(), getopt_long_only(): _GNU_SOURCE

       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.

       The variable optind is the index of the next element to be processed in
       argv.  The system initializes this value to 1.  The caller can reset it
       to 1 to restart scanning of the same argv, or when scanning a new argu-
       ment vector.

       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  (i.e.,  in the same word as the option name
       itself, for example, "-oarg"), then it is returned in optarg, otherwise
       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  scan-
       ning 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

       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 nonzero (which is the default), getopt()
       prints an error message.

   getopt_long() and getopt_long_only()
       The getopt_long() function works like  getopt()  except  that  it  also
       accepts long options, started with 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

       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

       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.

       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

       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 nonop-
              tion argument is encountered.

              This  variable  was  used by bash(1) 2.0 to communicate to glibc
              which arguments are the results of  wildcard  expansion  and  so
              should  not be considered as options.  This behavior was removed
              in bash(1) version 2.01, but the support remains in glibc.

       For  an  explanation  of  the  terms  used   in   this   section,   see

       |Interface                | Attribute     | Value                     |
       |getopt(), getopt_long(), | Thread safety | MT-Unsafe race:getopt env |
       |getopt_long_only()       |               |                           |
              POSIX.1-2001, POSIX.1-2008, and POSIX.2, provided  the  environ-
              ment  variable  POSIXLY_CORRECT is set.  Otherwise, the elements
              of argv aren't really const, because we permute them.   We  pre-
              tend  they're const in the prototype to be compatible with other

              The use of '+' and '-' in optstring is a GNU extension.

              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

       rechecks POSIXLY_CORRECT and checks for GNU extensions in optstring.)

       The following trivial example program uses getopt() to handle two  pro-
       gram  options:  -n, with no associated value; and -t val, which expects
       an associated value.

       #include <unistd.h>
       #include <stdlib.h>
       #include <stdio.h>

       main(int argc, char *argv[])
           int flags, opt;
           int nsecs, tfnd;

           nsecs = 0;
           tfnd = 0;
           flags = 0;
           while ((opt = getopt(argc, argv, "nt:")) != -1) {
               switch (opt) {
               case 'n':
                   flags = 1;
               case 't':
                   nsecs = atoi(optarg);
                   tfnd = 1;
               default: /* '?' */
                   fprintf(stderr, "Usage: %s [-t nsecs] [-n] name\n",

           printf("flags=%d; tfnd=%d; nsecs=%d; optind=%d\n",
                   flags, tfnd, nsecs, optind);

           if (optind >= argc) {
               fprintf(stderr, "Expected argument after options\n");

           printf("name argument = %s\n", argv[optind]);

           /* Other code omitted */


       The following example program illustrates the use of getopt_long() with
           while (1) {
               int this_option_optind = optind ? optind : 1;
               int option_index = 0;
               static struct option long_options[] = {
                   {"add",     required_argument, 0,  0 },
                   {"append",  no_argument,       0,  0 },
                   {"delete",  required_argument, 0,  0 },
                   {"verbose", no_argument,       0,  0 },
                   {"create",  required_argument, 0, 'c'},
                   {"file",    required_argument, 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);

               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 '?':


       getopt(1), getsubopt(3)

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       description of the project, information about reporting bugs,  and  the
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GNU                               2015-08-08                         GETOPT(3)
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