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
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 nonoptions 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 nonoption argument is encountered. If the first character
of
optstring is '-', then each nonoption
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.
While processing the option list,
getopt() can detect two kinds of
errors: (1) an option character that was not specified in
optstring and
(2) a missing option argument (i.e., an option at the end of the command line
without an expected argument). Such errors are handled and reported as
follows:
- *
- By default, getopt() prints an error message on standard error,
places the erroneous option character in optopt, and returns '?' as
the function result.
- *
- If the caller has set the global variable opterr to zero, then
getopt() does not print an error message. The caller can determine
that there was an error by testing whether the function return value is
'?'. (By default, opterr has a nonzero value.)
- *
- If the first character (following any optional '+' or '-' described above)
of optstring is a colon (':'), then getopt() likewise does
not print an error message. In addition, it returns ':' instead of '?' to
indicate a missing option argument. This allows the caller to distinguish
the two different types of errors.
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 nonoption
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.
For an explanation of the terms used in this section, see
attributes(7).
Interface |
Attribute |
Value |
getopt (), getopt_long (), getopt_long_only () |
Thread safety |
MT-Unsafe race:getopt env |
- getopt():
- POSIX.1-2001, POSIX.1-2008, and 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.
- 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.1-1996
marked the use of <stdio.h> for this purpose as LEGACY.
POSIX.1-2001 does not require 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 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; nsecs=%d; optind=%d\n",
flags, tfnd, nsecs, 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", required_argument, 0, 0 },
{"append", no_argument, 0, 0 },
{"delete", required_argument, 0, 0 },
{"verbose", no_argument, 0, 0 },
{"create", required_argument, 0, 'c'},
{"file", required_argument, 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);
}
getopt(1),
getsubopt(3)