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



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

SYNOPSIS
       #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 || _POSIX_SOURCE
       getopt_long(), getopt_long_only(): _GNU_SOURCE

DESCRIPTION
       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.

       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 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 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  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 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 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  non-zero  (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.

       has_arg
              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 lon-
       gopts.

       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.

RETURN VALUE
       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  opt-
       string,  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 parameter.

ENVIRONMENT
       POSIXLY_CORRECT
              If this is set, then option processing stops as soon as a non-option argument is encountered.

       _<PID>_GNU_nonoption_argv_flags_
              This variable was used by bash(1) 2.0 to communicate to glibc which arguments are the results  of  wild-
              card 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.

CONFORMING TO
       getopt():
              POSIX.2 and POSIX.1-2001, provided the environment variable POSIXLY_CORRECT is set.  Otherwise, the ele-
              ments  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.

NOTES
       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 resetting 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.)

BUGS
       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 speci-
       fied.

EXAMPLE
       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>

       int
       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;
                   break;
               case 't':
                   nsecs = atoi(optarg);
                   tfnd = 1;
                   break;
               default: /* '?' */
                   fprintf(stderr, "Usage: %s [-t nsecs] [-n] name\n",
                           argv[0]);
                   exit(EXIT_FAILURE);
               }
           }

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

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

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

           /* Other code omitted */

           exit(EXIT_SUCCESS);
       }

       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>

       int
       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)
                   break;

               switch (c) {
               case 0:
                   printf("option %s", long_options[option_index].name);
                   if (optarg)
                       printf(" with arg %s", optarg);
                   printf("\n");
                   break;

               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);
                   break;

               case 'a':
                   printf("option a\n");
                   break;

               case 'b':
                   printf("option b\n");
                   break;

               case 'c':
                   printf("option c with value '%s'\n", optarg);
                   break;

               case 'd':
                   printf("option d with value '%s'\n", optarg);
                   break;

               case '?':
                   break;

               default:
                   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(EXIT_SUCCESS);
       }

SEE ALSO
       getsubopt(3), feature_test_macros(7)

COLOPHON
       This  page  is part of release 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



GNU                               2008-08-29                         GETOPT(3)