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NAME

       getopt - 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;

       #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);

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.

       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, 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  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
       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.

       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.

       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 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.

RETURN VALUE

       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 -1 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 -1 returns are the same as
       for  getopt(),  plus  ‘?’  for  an  ambiguous  match  or  an extraneous
       parameter.

ENVIRONMENT VARIABLES

       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 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.

EXAMPLE

       The following example program, from the source  code,  illustrates  the
       use of getopt_long() with most of its features.

       #include <stdio.h>

       int
       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)
            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 (0);
       }

BUGS

       This manpage is confusing.

       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 behaviour rather than
       that specified.

CONFORMING TO

       getopt():
              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.

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