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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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