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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;

       #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 (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
       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 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

       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
       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 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.

CONFORMING TO

       getopt():
              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>.

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 specified.

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

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