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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
''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
____ 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 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 (0);
       }

An short and sweet example of getopt usage:
    int ch; /* Butchered out of [tcpperf|http://www.wand.net.nz/~stj2/nsc/software.html] by SamJansen */
    while ((ch = getopt(argc, argv, "c:p:s:")) != -1)
        switch (ch) {
            case 'c':
                /* Client machine to connect to */
                client = optarg;
                break;
            case 'p':
                /* port */
                port = atoi(optarg);
                break;
            case 's':
                write_size = atoi(optarg);
                break;
            case '?':
            default:
                usage(argv[[0]);
        }
    argc -= optind;
    argv += optind;



!!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 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.

----

!NOTES

! getopt keeps internal state

If you want to use getopt more than once within a program, across different inputs, you'll need to reset its internal state counters before
each use:

<pre>
	printf("%d %d %d\n",optind,opterr,optopt);
        ... do getopt stuff ...
        printf("%d %d %d\n",optind,opterr,optopt);
</pre>

This outputs the following:

<pre>
1 1 63
3 1 63
</pre>

the '3' in my case is because I only had one option + parameter (+ program name == 3).

So, if you reset optind, opterr and optopt to 1, 1 and 63, before each new use of getopt, you should be fine.

-- DanielLawson
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Last edited on Tuesday, November 9, 2004 9:41:04 am by DanielLawson
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