GETOPT_LONG(3C) Standard C Library Functions GETOPT_LONG(3C)


getopt_long, getopt_long_clip, getopt_long_only - get long options from
command line argument list


#include <getopt.h>

extern char *optarg;
extern int optind;
extern int optopt;
extern int opterr;

getopt_long(int argc, char * const *argv, const char *optstring,
const struct option *longopts, int *longindex);

getopt_long_only(int argc, char * const *argv, const char *optstring,
const struct option *longopts, int *longindex);

getopt_long_clip(int argc, char * const *argv, const char *optstring,
const struct option *longopts, int *longindex);


The getopt_long() function is similar to getopt(3C) but it accepts options
in two forms: short options and long options. Short options are the
traditional option flags that use a hyphen followed by a single character.
This is the only form of option that is portable and it is supported by
getopt(3C). Note, some implementation of getopt(3C) do support non-
standard extensions for long options; however, these are not portable and
not considered in this manual page. Common example of short options are:
-a, -l, and -r. Long options use two hyphen characters are generally full
words. The long versions of the above might be: --all, --list, and

The getopt_long() function can be used to:

1. Support an option with both short and long forms.

2. Support an option with only a short form.

3. Support an option with only a long form.

To have a short option selected, as with getopt(3C), it must be listed in
optstring. Long options are instead listed in the longopts array. For an
option to have both a short and long form it must be present in both
optstring and longopts.

Long options can be handled in two different ways. In the first way, every
long option understood by the program has a corresponding short option, and
the option structure is only used to translate from long options to short
options. When used in this fashion, getopt_long() behaves identically to
getopt(3C). This is a good way to add long option processing to an
existing program with the minimum of rewriting.

In the second mechanism, a long option sets a flag in the option structure
passed, or will store a pointer to the command line argument in the option
structure passed to it for options that take arguments. Additionally, the
long option's argument may be specified as a single argument with an equal
sign, e.g.,

myprogram --myoption=somevalue

When a long option is processed, the call to getopt_long() will return 0.
For this reason, long option processing without shortcuts is not backwards
compatible with getopt(3C).

It is possible to combine these methods, providing for long options
processing with short option equivalents for some options. Less frequently
used options would be processed as long options only.

In getopt_long() and getopt_long_only(), optstring acts similar to
optstring in getopt(3C), listing the set of supported short option flags.
In addition, optstring can begin with `+' or `-'. If optstring begins with
`+', the first non-option terminates option processing. This is equivalent
to setting the environment variable POSIXLY_CORRECT. If optstring begins
with `-', non-options are treated as options to the argument `\1'.

If optstring does not begin with `+' and POSIXLY_CORRECT is not set, if
`W;' appears in optstring, `-W myoption' is treated the same as
`--myoption' and optarg is set to `myoption'.

In getopt_long_clip(), `+' and `-' are ignored at the beginning of a

The getopt_long(), getopt_long_only(), and getopt_long_clip() functions
require a structure to be initialized describing the long options. The
structure is:

struct option {
char *name;
int has_arg;
int *flag;
int val;

The name field should contain the option name without the leading double

The has_arg field should be one of:

no_argument no argument to the option is expected
required_argument an argument to the option is required
optional_argument an argument to the option may be presented

If flag is not NULL, then the integer pointed to by it will be set to the
value in the val field and optopt will be set to 0. If the flag field is
NULL, then the val field will be returned and optopt is set to the value in
the val field. Setting flag to NULL and setting val to the corresponding
short option will make this function act just like getopt(3C).

If the longindex field is not NULL, then the integer pointed to by it will
be set to the index of the long option relative to longopts.

The last element of the longopts array has to be filled with zeroes.

The getopt_long_only() function behaves identically to getopt_long() with
the exception that long options may start with `-' in addition to `--'. If
an option starting with `-' does not match a long option but does match a
single-character option, the single-character option is returned.

The getopt_long_clip() function is a variation of getopt_long() except that
options must also adhere to the Sun CLIP specification. Specifically, the
major differences from getopt_long() are:

+o All option arguments are required (optional_argument is treated
the same as required_argument).

+o Long options cannot be abbreviated on the command line.

+o Long options must use a double hyphen (`--').

+o Option processing stops at the first non-option.

+o All long options must have an equivalent short option (single
character) and vice-versa.

+o A leading `+' or `-' in optstring is ignored. optstring is
treated as if it began after the leading `+' or `-'.

On each call to getopt_long(), getopt_long_only(), or getopt_long(), optind
is set to the argv index of the next argument to be processed. optind is
initialized to 1 prior to the first invocation of getopt_long(),
getopt_long_only(), or getopt_long_clip().

If opterr is set to a non-zero value and optstring does not start with `:',
getopt_long(), getopt_long_only(), and getopt_long_clip() will print an
error message to stderr when an error or invalid option is encountered.


If the flag field in struct option is NULL, getopt_long() and
getopt_long_only() return the value specified in the val field, which is
usually just the corresponding short option. If flag is not NULL, these
functions return 0 and store val in the location pointed to by flag. These
functions return `:' if there was a missing option argument, `?' if the
user specified an unknown or ambiguous option, and -1 when the argument
list has been exhausted.

If a long option to getopt_long_clip() is missing its equivalent short
option (or vice-versa),-1 is returned on the first call to
getopt_long_clip(), and errno is set to EINVAL. If opterr is set to a non-
zero value and optstring does not start with `:', an error message will be
written to stderr.

If optstring does not start with `:' and getopt_long(), getopt_long_only(),
or getopt_long_clip() return `:' or `?', if opterr is set to a non-zero
value, an error message is written to stderr.


The following environment variables can effect the execution of
getopt_long, getopt_long_only, and getopt_long_clip: LANG, LC_ALL,
LC_MESSAGES. See environ(7).

POSIXLY_CORRECT If set, option processing stops when the first non-
option is found and a leading `-' or `+' in the
optstring is ignored.


Similar to getopt(3C), since there is no unambiguous way to detect a
missing option-argument except when the option is the last option on the
command line, the getopt_long(), getopt_long_only(), and getopt_long_clip()
functions cannot fully check for mandatory arguments. For example, the
option string `ho:' with an input of `-o -h' will assume that `-h' is the
required argument to -o instead of assuming that -o is missing its option-

Like getopt(3C), grouping options taking or requiring arguments with other
options is a violation of the Basic Utility Command syntax standard (see
Intro(1)). For example, given the option string `cde:', running:

cmd -cde ieio

is incorrect. Current versions of getopt_long, getopt_long_only, and
getopt_long_clip accept this, however future versions may not support this.
The correct invocation would be:

cmd -cd -e ieio


Example 1 Basic usage of getopt_long().

In this example, the short options, -b and -f are treated the same way as
their corresponding long options --buffy and --fluoride. The long option
--daggerset is only matched as a long option.

int bflag, ch, fd;
int daggerset;

/* options descriptor */
static struct option longopts[] = {
{ "buffy", no_argument, NULL, 'b' },
{ "fluoride", required_argument, NULL, 'f' },
{ "daggerset", no_argument, &daggerset, 1 },
{ NULL, 0, NULL, 0 }

bflag = 0;
while ((ch = getopt_long(argc, argv, "bf:", longopts, NULL)) != -1) {
switch (ch) {
case 'b':
bflag = 1;
case 'f':
if ((fd = open(optarg, O_RDONLY, 0)) == -1)
err(1, "unable to open %s", optarg);
case 0:
if (daggerset) {
fprintf(stderr,"Buffy will use her dagger to "
"apply fluoride to dracula's teeth\n");
argc -= optind;
argv += optind;

Example 2 Mixing short-only and long-only options.

This example has a program that uses both short and long options and always
causes the option to be handled in a way that is similar to getopt(3C)
regardless of if it is short or long. Options that are only long options
are assigned a character value that is outside of the common 8-bit range
(starting at USHRT_MAX + 1.) This allows them to still integrate into a
normal getopt(3C) style option processing loop.

In the following code, -s is only usable as a short option while
--long-only is only usable as a long option, hence -s is only specified in
optstring and --long-only is only specified in the longopts option array.

#include <getopt.h>
#include <stdio.h>
#include <limits.h>

enum longopt_chars {

static struct option longopts[] = {
{ "all", no_argument, NULL, 'a' },
{ "list", no_argument, NULL, 'l' },
{ "long-only", no_argument, NULL, LONG_ONLY },
{ "output", required_argument, NULL, 'o' },
{ NULL }

main(int argc, char *argv[])
int ch;

while ((ch = getopt_long(argc, argv, "alo:s", longopts,
NULL)) != -1) {
switch (ch) {
case 'a':
printf("found -a\n");
case 'l':
printf("found -l\n");
case 'o':
printf("found -o: %s\n", optarg);
case 's':
printf("found -s\n");
printf("found --long-only\n");

return (0);


The getopt_long_clip() function will fail if:

EINVAL A short option is missing a corresponding long option, or vice-

There are no errors defined for getopt_long() and getopt_long_only().


While the illumos implementations of getopt_long and getopt_long_only are
broadly compatible with other implementations, the following edge cases
have historically been known to vary among implementations:

+o The setting of optopt for long options with flag != NULL in struct
option. In illumos, optopt is set to 0 (since val would never be

+o The setting of optarg for long options without an argument that are
invoked via `-W' (`W;' in optstring). illumos sets optarg to the
option name (the argument of `-W').

+o The handling of `-W' with an argument that is not (a prefix to) a known
long option (`W;' in optstring). illumos treats this as an error
(unknown option) and returns `?' with optopt set to 0 and optarg set to

+o illumos may not permute the argument vector at the same points in the
calling sequence as other implementations. The aspects normally used
by the caller (ordering after -1 is returned, the value of optind
relative to current positions) are the same, though. (We often do
fewer variable swaps.)







The argv argument is not really const as its elements may be permuted
(unless POSIXLY_CORRECT is set).

OmniOS August 10, 2020 OmniOS