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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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RUBENS DE JESUS NOGUEIRA <darkseid99@usa.net> (tradução) XXXXXX XX XXXXX XXXXXXXX <xxxxxxxxxx@xxx.xxx>
(revisão)
GNU 8 May 1998 GETOPT(3)