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GETOPT(3) Linux Programmer's Manual GETOPT(3)
getopt, getopt_long, getopt_long_only, optarg, optind, opterr, optopt - Parse
command-line options
#include <unistd.h>
int getopt(int argc, char * const argv[],
const char *optstring);
extern char *optarg;
extern int optind, opterr, optopt;
#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);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
getopt(): _POSIX_C_SOURCE >= 2 || _XOPEN_SOURCE || _POSIX_SOURCE
getopt_long(), getopt_long_only(): _GNU_SOURCE
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.
The variable optind is the index of the next element to be processed in argv.
The system initializes this value to 1. The caller can reset it to 1 to
restart scanning of the same argv, or when scanning a new argument vector.
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.
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.
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.
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.
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.
The use of '+' and '-' in optstring is a GNU extension.
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>.
getopt_long() and getopt_long_only():
These functions are GNU extensions.
A program that scans multiple argument vectors, or rescans the same vector
more than once, and wants to make use of GNU extensions such as '+' and '-' at
the start of optstring, or changes the value of POSIXLY_CORRECT between scans,
must reinitialize getopt() by resetting optind to 0, rather than the
traditional value of 1. (Resetting to 0 forces the invocation of an internal
initialization routine that rechecks POSIXLY_CORRECT and checks for GNU
extensions in optstring.)
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.
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);
}
getsubopt(3), feature_test_macros(7)
This page is part of release 3.21 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
GNU 2008-08-29 GETOPT(3)