'\" t
.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH getopt_long 3 2025-12-25 "Linux man-pages (unreleased)"
.SH NAME
getopt_long
\- parse command-line options
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.B #define _GNU_SOURCE
.B #include <getopt.h>
.P
.BI "int getopt_long(int " argc ", char *" argv [],
.BI "           const char *" optstring ,
.BI "           const struct option *" longopts ", int *" longindex );
.fi
.SH DESCRIPTION
The
.BR getopt_long ()
function works like
.BR getopt (3)
except that it also accepts long options, started with two dashes.
(If the program accepts only long options, then
.I 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
.B \-\-arg=param
or
.BR "\-\-arg param" .
.P
.I longopts
is a pointer to the first element of an array of
.I struct option
declared in
.I <getopt.h>
as
.P
.in +4n
.EX
struct option {
    const char *name;
    int         has_arg;
    int        *flag;
    int         val;
};
.EE
.in
.P
The meanings of the different fields are:
.TP
.I name
is the name of the long option.
.TP
.I has_arg
is:
.B no_argument
(or 0) if the option does not take an argument;
.B required_argument
(or 1) if the option requires an argument;
or
.B optional_argument
(or 2) if the option takes an optional argument.
.TP
.I flag
specifies how results are returned for a long option.
If
.I flag
is NULL, then
.BR getopt_long ()
returns
.IR val .
(For example, the calling program may set
.I val
to the equivalent short
option character.)
Otherwise,
.BR getopt_long ()
returns 0, and
.I flag
points to a variable which is set to
.I val
if the option is found,
but left unchanged if the option is not found.
.TP
.I val
is the value to return, or to load into the variable pointed
to by
.IR flag .
.P
The last element of the array has to be filled with zeros.
.P
If
.I longindex
is not NULL, it
points to a variable which is set to the index of the long option relative to
.IR longopts .
.P
Its analogue to
.BR getopt (3)'s
.I optopt
is
.RI \[lq] "argv[(optind \- 1)]" \[rq].
.SH RETURN VALUE
See
.BR getopt (3).
.P
.BR getopt_long ()
also returns the option
character when a short option is recognized.
For a long option,
it returns
.I val
if
.I flag
is NULL, and 0 otherwise.
Error and \-1 returns are the same as for
.BR getopt (3),
plus \[aq]?\[aq] for an
ambiguous match or an extraneous parameter.
.SH ENVIRONMENT
See
.BR getopt (3).
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lb lb lbx
l l l.
Interface	Attribute	Value
T{
.na
.nh
.BR getopt_long ()
T}	Thread safety	T{
.na
.nh
MT-Unsafe race:getopt env
T}
.TE
.SH STANDARDS
GNU.
.SH EXAMPLES
The following example program illustrates the use of
.BR getopt_long ()
with most of its features.
.P
.\" SRC BEGIN (getopt_long.c)
.EX
#include <getopt.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.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, \[aq]c\[aq]},
            {"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("\[rs]n");
            break;
\&
        case \[aq]0\[aq]:
        case \[aq]1\[aq]:
        case \[aq]2\[aq]:
            if (digit_optind != 0 && digit_optind != this_option_optind)
              printf("digits occur in two different argv\-elements.\[rs]n");
            digit_optind = this_option_optind;
            printf("option %c\[rs]n", c);
            break;
\&
        case \[aq]a\[aq]:
            printf("option a\[rs]n");
            break;
\&
        case \[aq]b\[aq]:
            printf("option b\[rs]n");
            break;
\&
        case \[aq]c\[aq]:
            printf("option c with value \[aq]%s\[aq]\[rs]n", optarg);
            break;
\&
        case \[aq]d\[aq]:
            printf("option d with value \[aq]%s\[aq]\[rs]n", optarg);
            break;
\&
        case \[aq]?\[aq]:
            break;
\&
        default:
            printf("?? getopt returned character code 0%o ??\[rs]n", c);
        }
    }
\&
    if (optind < argc) {
        printf("non\-option ARGV\-elements: ");
        while (optind < argc)
            printf("%s ", argv[optind++]);
        printf("\[rs]n");
    }
\&
    exit(EXIT_SUCCESS);
}
.EE
.\" SRC END
.SH SEE ALSO
.BR getopt (1),
.BR getopt (3),
.BR getopt_long_only (3),
.BR getsubopt (3)