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

NAME

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

SYNOPSIS

#include <getopt.h>

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

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);

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

DESCRIPTION

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 --recursive.

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
string.

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 hyphen.

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.

RETURN VALUES

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.

ENVIRONMENT

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.

USAGE

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-argument.

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

EXAMPLES

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;
break;
case 'f':
if ((fd = open(optarg, O_RDONLY, 0)) == -1)
err(1, "unable to open %s", optarg);
break;
case 0:
if (daggerset) {
fprintf(stderr,"Buffy will use her dagger to "
"apply fluoride to dracula's teeth\n");
}
break;
default:
usage();
}
}
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 {
LONG_ONLY = USHRT_MAX +1
};

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 }
};

int
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");
break;
case 'l':
printf("found -l\n");
break;
case 'o':
printf("found -o: %s\n", optarg);
break;
case 's':
printf("found -s\n");
break;
case LONG_ONLY:
printf("found --long-only\n");
break;
default:
break;
}
}

return (0);
}

ERRORS

The getopt_long_clip() function will fail if:

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

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

IMPLEMENTATION DIFFERENCES

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
returned).

+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 NULL.

+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.)

INTERFACE STABILITY

Committed

MT-LEVEL
Unsafe

SEE ALSO

getopt(3C)

BUGS

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

illumos August 10, 2020 illumos