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

       getopt, getopt_long, getopt_long_only, optarg, optind, opterr, optopt - Parse command-line

       #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  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.

       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 argument vector.

       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 (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 behav‐
       ior 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
       nonoptions  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 nonoption argument is encountered.  If the first character of
       optstring is '-', then each nonoption 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 (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 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 zeros.

       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()  encoun‐
       ters 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 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 parameter.

              If  this  is  set,  then option processing stops as soon as a nonoption argument is

              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.

              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  allow  the
              declaration to appear in <stdio.h>.

       getopt_long() and getopt_long_only():
              These functions are GNU extensions.

       A program that scans multiple argument vectors, or rescans the same vector more than once,
       and wants to make use of GNU extensions such as '+' and '-' at the start of optstring,  or
       changes  the  value of POSIXLY_CORRECT between scans, must reinitialize getopt() by reset‐
       ting optind to 0, rather than the traditional value of 1.   (Resetting  to  0  forces  the
       invocation  of an internal initialization routine that rechecks POSIXLY_CORRECT and checks
       for GNU extensions in optstring.)

       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 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 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",     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 '?':

                   printf("?? getopt returned character code 0%o ??\n", c);

           if (optind < argc) {
               printf("non-option ARGV-elements: ");
               while (optind < argc)
                   printf("%s ", argv[optind++]);



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GNU                                         2014-05-09                                  GETOPT(3)

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