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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ENVIRONMENT | ATTRIBUTES | STANDARDS | EXAMPLES | SEE ALSO | COLOPHON |
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getopt_long(3) Library Functions Manual getopt_long(3)
getopt_long - parse command-line options
Standard C library (libc, -lc)
#define _GNU_SOURCE
#include <getopt.h>
int getopt_long(int argc, char *argv[],
const char *optstring,
const struct option *longopts, int *longindex);
The getopt_long() function works like getopt(3) 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.
Its analogue to getopt(3)'s optopt is “argv[(optind - 1)]”.
See getopt(3).
getopt_long() also returns the option character when a short
option is recognized. For a long option, it returns val if flag
is NULL, and 0 otherwise. Error and -1 returns are the same as
for getopt(3), plus '?' for an ambiguous match or an extraneous
parameter.
See getopt(3).
For an explanation of the terms used in this section, see
attributes(7).
┌───────────────┬───────────────┬────────────────────────────────┐
│ Interface │ Attribute │ Value │
├───────────────┼───────────────┼────────────────────────────────┤
│ getopt_long() │ Thread safety │ MT-Unsafe race:getopt env │
└───────────────┴───────────────┴────────────────────────────────┘
GNU.
The following example program illustrates the use of getopt_long()
with most of its features.
#include <getopt.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int
main(int argc, char *argv[])
{
int c;
int digit_optind = 0;
for (;;) {
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), getopt(3), getopt_long_only(3), getsubopt(3)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.18.tar.gz
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⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2026-05-24. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
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part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.18 2026-02-14 getopt_long(3)
Pages that refer to this page: tcpdump(1), getopt(3), getopt_long_only(3), pmgetoptions(3), tcpdump(8)
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HTML rendering created 2026-05-24 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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