GETOPT(3) Linux Programmer's Manual GETOPT(3)
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 invoca-
tion. An element of argv that starts with `-' (and is not
exactly "-" or "--") is an option element. The characters
of this element (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
characters. 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.
By default, getargs() permutes the contents of argv as it
scans, so that eventually all the non-options are at the
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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 character 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 written to expect options and other argv-ele-
ments 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
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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 other-
wise. Error and EOF returns are the same as for getopt(),
plus `?' for an ambiguous match or an extraneous parame-
ter.
ENVIRONMENT VARIABLES
POSIXLY_CORRECT
If this is set, then option processing stops as
soon as a non-option argument is encountered.
EXAMPLE
The following example program, from the source code,
illustrates the use of getopt_long() with most of its fea-
tures.
#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},
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{"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);
}
}
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if (optind < argc)
{
printf ("non-option ARGV-elements: ");
while (optind < argc)
printf ("%s ", argv[optind++]);
printf ("\n");
}
exit (0);
}
BUGS
This manpage is confusing.
CONFORMING TO
getopt():
POSIX.1, 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.
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