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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ENVIRONMENT | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON |
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
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.
getopt_long() and getopt_long_only()
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(), │ Thread safety │ MT-Unsafe race:getopt env │
│getopt_long_only() │ │ │
└─────────────────────────┴───────────────┴───────────────────────────┘
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.)
getopt()
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);
}
getopt_long()
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)
This page is part of release 4.12 of the Linux man-pages project. A
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latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
GNU 2017-03-13 GETOPT(3)
Pages that refer to this page: getopt(1), execve(2), getsubopt(3), pmdagetoptions(3), pmgetoptions(3), groff_tmac(5)