NAME
getopt - Parse command line options
SYNOPSIS
#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));
DESCRIPTION
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 ele-
ment (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.
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
EOF. 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 char-
acters. 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, it is returned in optarg, otherwise
optarg is set to zero. This is a GNU extension. If opt-
string 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
behaviour is a GNU extension, not available with libraries
before GNU libc 2.
By default, getopt() permutes the contents of argv as it
scans, so that eventually all the non-options 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 non-option argument is encountered. If the first char-
acter of optstring is `-', then each non-option argv-element
is handled as if it were the argument of an option with
character code 1. (This is used by programs that were writ-
ten 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.
If getopt() does not recognize an option character, it
prints an error message to stderr, stores the character in
optopt, and returns `?'. The calling program may prevent
the error message by setting opterr to 0.
The getopt_long() function works like getopt() except that
it also accepts long options, started out by two dashes.
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 zeroes.
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.
RETURN VALUE
The getopt() function returns the option character if the
option was found successfully, `:' if there was a missing
parameter for one of the options, `?' for an unknown option
character, or EOF for the end of the option list.
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 EOF returns are the same as for getopt(), plus `?'
for an ambiguous match or an extraneous parameter.
ENVIRONMENT VARIABLES
POSIXLY_CORRECT
If this is set, then option processing stops as soon as
a non-option argument is encountered.
_<PID>_GNU_nonoption_argv_flags_
This variable was used by bash 2.0 to communicate to
GNU libc which arguments are the results of wildcard
expansion and so should not be considered as options.
This behaviour was removed in bash version 2.01, but
the support remains in GNU libc.
EXAMPLE
The following example program, from the source code, illus-
trates the use of getopt_long() with most of its features.
#include <stdio.h>
int
main (argc, argv)
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", 1, 0, 0},
{"append", 0, 0, 0},
{"delete", 1, 0, 0},
{"verbose", 0, 0, 0},
{"create", 1, 0, 'c'},
{"file", 1, 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 (0);
}
BUGS
This manpage is confusing.
The POSIX.2 specification of getopt() has a technical error
described in POSIX.2 Interpretation 150. The GNU implemen-
tation (and probably all other implementations) implements
the correct behaviour rather than that specified.
CONFORMING TO
getopt():
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.