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       getopt, getopt_long, getopt_long_only - 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
       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 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
       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 (i.e., in the same word as the option
       name itself, for example, "-oarg"), then  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 behavior  is  a  GNU  extension,  not
       available with libraries before glibc 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

       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.

       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

       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.


       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
       character  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


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


              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>.


       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 behavior rather than
       that specified.


       The following trivial example  program  uses  getopt()  to  handle  two
       program  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; optind=%d\n", flags, tfnd, 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
       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);

               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++]);



       getsubopt(3), feature_test_macros(7)


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