Originální popis anglicky:
getopt - Parse command line options
Návod, kniha: Linux Programmer's Manual
#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);
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.
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 nonzero (which is the default),
getopt() prints an error message.
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.
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.
- 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.
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);
}
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.
- 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.
