path: root/man3/getopt.3

.\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
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.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\" License.
.\" Modified Sat Jul 24 19:27:50 1993 by Rik Faith (faith@cs.unc.edu)
.\" Modified Mon Aug 30 22:02:34 1995 by Jim Van Zandt <jrv@vanzandt.mv.com>
.\"  longindex is a pointer, has_arg can take 3 values, using consistent
.\"  names for optstring and longindex, "\n" in formats fixed.  Documenting
.\"  opterr and getopt_long_only.  Clarified explanations (borrowing heavily
.\"  from the source code).
.\" Modified 8 May 1998 by Joseph S. Myers (jsm28@cam.ac.uk)
.\" Modified 990715, aeb: changed `EOF' into `-1' since that is what POSIX
.\"  says; moreover, EOF is not defined in <unistd.h>.
.\" Modified 2002-02-16, joey: added information about nonexistent
.\"  option character and colon as first option character
.\" Modified 2004-07-28, Michael Kerrisk <mtk.manpages@gmail.com>
.\"	Added text to explain how to order both '[-+]' and ':' at
.\"		the start of optstring
.\" Modified 2006-12-15, mtk, Added getopt() example program.
.\"
.TH GETOPT 3  2010-11-01 "GNU" "Linux Programmer's Manual"
.SH NAME
getopt, getopt_long, getopt_long_only,
optarg, optind, opterr, optopt \- Parse command-line options
.SH SYNOPSIS
.nf
.B #include <unistd.h>
.sp
.BI "int getopt(int " argc ", char * const " argv[] ,
.BI "           const char *" optstring );
.sp
.BI "extern char *" optarg ;
.BI "extern int " optind ", " opterr ", " optopt ;
.sp
.B #include <getopt.h>
.sp
.BI "int getopt_long(int " argc ", char * const " argv[] ,
.BI "           const char *" optstring ,
.BI "           const struct option *" longopts ", int *" longindex );
.sp
.BI "int getopt_long_only(int " argc ", char * const " argv[] ,
.BI "           const char *" optstring ,
.BI "           const struct option *" longopts ", int *" longindex );
.fi
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.ad l
.in
.sp
.BR getopt ():
_POSIX_C_SOURCE\ >=\ 2 || _XOPEN_SOURCE
.br
.BR getopt_long (),
.BR getopt_long_only ():
_GNU_SOURCE
.ad b
.SH DESCRIPTION
The
.BR getopt ()
function parses the command-line arguments.
Its arguments
.I argc
and
.I argv
are the argument count and array as passed to the
.IR main ()
function on program invocation.
An element of \fIargv\fP that starts with \(aq\-\(aq
(and is not exactly "\-" or "\-\-")
is an option element.
The characters of this element
(aside from the initial \(aq\-\(aq) are option characters.
If
.BR getopt ()
is called repeatedly, it returns successively each of the option characters
from each of the option elements.
.PP
The variable
.I optind
is the index of the next element to be processed in
.IR argv .
The system initializes this value to 1.
The caller can reset it to 1 to restart scanning of the same
.IR argv ,
or when scanning a new argument vector.
.PP
If
.BR getopt ()
finds another option character, it returns that
character, updating the external variable \fIoptind\fP and a static
variable \fInextchar\fP so that the next call to
.BR getopt ()
can
resume the scan with the following option character or
\fIargv\fP-element.
.PP
If there are no more option characters,
.BR getopt ()
returns \-1.
Then \fIoptind\fP is the index in \fIargv\fP of the first
\fIargv\fP-element that is not an option.
.PP
.I optstring
is a string containing the legitimate option characters.
If such a
character is followed by a colon, the option requires an argument, so
.BR getopt ()
places a pointer to the following text in the same
\fIargv\fP-element, or the text of the following \fIargv\fP-element, in
.IR optarg .
Two colons mean an option takes
an optional arg; if there is text in the current \fIargv\fP-element
(i.e., in the same word as the option name itself, for example, "\-oarg"),
then it is returned in \fIoptarg\fP, otherwise \fIoptarg\fP is set to zero.
This is a GNU extension.
If
.I optstring
contains
.B W
followed by a semicolon, then
.B \-W foo
is treated as the long option
.BR \-\-foo .
(The
.B \-W
option is reserved by POSIX.2 for implementation extensions.)
This behavior is a GNU extension, not available with libraries before
glibc 2.
.PP
By default,
.BR getopt ()
permutes the contents of \fIargv\fP as it
scans, so that eventually all the nonoptions are at the end.
Two other modes are also implemented.
If the first character of
\fIoptstring\fP is \(aq+\(aq or the environment variable
.B POSIXLY_CORRECT
is set, then option processing stops as soon as a nonoption argument is
encountered.
If the first character of \fIoptstring\fP is \(aq\-\(aq, then
each nonoption \fIargv\fP-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 \fIargv\fP-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.
.PP
If
.BR getopt ()
does not recognize an option character, it prints an
error message to \fIstderr\fP, stores the character in \fIoptopt\fP, and
returns \(aq?\(aq.
The calling program may prevent the error message by
setting \fIopterr\fP to 0.
.PP
If
.BR getopt ()
finds an option character in \fIargv\fP that was not
included in \fIoptstring\fP, or if it detects a missing option argument,
it returns \(aq?\(aq and sets the external variable \fIoptopt\fP to the
actual option character.
If the first character
(following any optional \(aq+\(aq or \(aq\-\(aq described above)
of \fIoptstring\fP
is a colon (\(aq:\(aq), then
.BR getopt ()
returns \(aq:\(aq instead of \(aq?\(aq to
indicate a missing option argument.
If an error was detected, and
the first character of \fIoptstring\fP is not a colon, and
the external variable \fIopterr\fP is nonzero (which is the default),
.BR getopt ()
prints an error message.
.SS getopt_long() and getopt_long_only()
The
.BR getopt_long ()
function works like
.BR getopt ()
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" .
.PP
.I longopts
is a pointer to the first element of an array of
.I struct option
declared in
.I <getopt.h>
as
.in +4n
.nf
.sp
struct option {
    const char *name;
    int         has_arg;
    int        *flag;
    int         val;
};
.fi
.in
.PP
The meanings of the different fields are:
.TP
.I name
is the name of the long option.
.TP
.I has_arg
is:
\fBno_argument\fP (or 0) if the option does not take an argument;
\fBrequired_argument\fP (or 1) if the option requires an argument; or
\fBoptional_argument\fP (or 2) if the option takes an optional argument.
.TP
.I flag
specifies how results are returned for a long option.
If \fIflag\fP
is NULL, then
.BR getopt_long ()
returns \fIval\fP.  (For
example, the calling program may set \fIval\fP to the equivalent short
option character.)
Otherwise,
.BR getopt_long ()
returns 0, and
\fIflag\fP points to a variable which is set to \fIval\fP if the
option is found, but left unchanged if the option is not found.
.TP
\fIval\fP
is the value to return, or to load into the variable pointed
to by \fIflag\fP.
.PP
The last element of the array has to be filled with zeros.
.PP
If \fIlongindex\fP is not NULL, it
points to a variable which is set to the index of the long option relative to
.IR longopts .
.PP
.BR getopt_long_only ()
is like
.BR getopt_long (),
but \(aq\-\(aq as well
as "\-\-" can indicate a long option.
If an option that starts with \(aq\-\(aq
(not "\-\-") doesn't match a long option, but does match a short option,
it is parsed as a short option instead.
.SH RETURN VALUE
If an option was successfully found, then
.BR getopt ()
returns the option character.
If all command-line options have been parsed, then
.BR getopt ()
returns \-1.
If
.BR getopt ()
encounters an option character that was not in
.IR optstring ,
then \(aq?\(aq is returned.
If
.BR getopt ()
encounters an option with a missing argument,
then the return value depends on the first character in
.IR optstring :
if it is \(aq:\(aq, then \(aq:\(aq is returned; otherwise \(aq?\(aq is returned.
.PP
.BR getopt_long ()
and
.BR getopt_long_only ()
also return the option
character when a short option is recognized.
For a long option, they
return \fIval\fP if \fIflag\fP is NULL, and 0 otherwise.
Error and \-1 returns are the same as for
.BR getopt (),
plus \(aq?\(aq for an
ambiguous match or an extraneous parameter.
.SH ENVIRONMENT
.TP
.B POSIXLY_CORRECT
If this is set, then option processing stops as soon as a nonoption
argument is encountered.
.TP
.B _<PID>_GNU_nonoption_argv_flags_
This variable was used by
.BR bash (1)
2.0 to communicate to glibc which arguments are the results of
wildcard expansion and so should not be considered as options.
This behavior was removed in
.BR bash (1)
version 2.01, but the support remains in glibc.
.SH CONFORMING TO
.TP
.BR getopt ():
POSIX.2 and POSIX.1-2001,
provided the environment variable
.B POSIXLY_CORRECT
is set.
Otherwise, the elements of \fIargv\fP aren't really const, because we
permute them.
We pretend they're const in the prototype to be
compatible with other systems.

The use of \(aq+\(aq and \(aq\-\(aq in
.I optstring
is a GNU extension.

On some older implementations,
.BR getopt ()
was declared in
.IR <stdio.h> .
SUSv1 permitted the declaration to appear in either
.I <unistd.h>
or
.IR <stdio.h> .
POSIX.1-2001 marked the use of
.I <stdio.h>
for this purpose as LEGACY.
POSIX.1-2001 does not allow the declaration to appear in
.IR <stdio.h> .
.TP
.BR getopt_long "() and " getopt_long_only ():
These functions are GNU extensions.
.SH NOTES
A program that scans multiple argument vectors,
or rescans the same vector more than once,
and wants to make use of GNU extensions such as \(aq+\(aq
and \(aq\-\(aq at the start of
.IR optstring ,
or changes the value of
.B POSIXLY_CORRECT
between scans,
must reinitialize
.BR getopt ()
by resetting
.I optind
to 0, rather than the traditional value of 1.
(Resetting to 0 forces the invocation of an internal initialization
routine that rechecks
.B POSIXLY_CORRECT
and checks for GNU extensions in
.IR optstring .)
.SH BUGS
The POSIX.2 specification of
.BR getopt ()
has a technical error described in POSIX.2 Interpretation 150.
The GNU
implementation (and probably all other implementations) implements the
correct behavior rather than that specified.
.SH EXAMPLE
The following trivial example program uses
.BR getopt ()
to handle two program options:
.IR \-n ,
with no associated value; and
.IR "\-t val" ,
which expects an associated value.
.nf
.sp
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>

int
main(int argc, char *argv[])
{
    int flags, opt;
    int nsecs, tfnd;

    nsecs = 0;
    tfnd = 0;
    flags = 0;
    while ((opt = getopt(argc, argv, "nt:")) != \-1) {
        switch (opt) {
        case \(aqn\(aq:
            flags = 1;
            break;
        case \(aqt\(aq:
            nsecs = atoi(optarg);
            tfnd = 1;
            break;
        default: /* \(aq?\(aq */
            fprintf(stderr, "Usage: %s [\-t nsecs] [\-n] name\\n",
                    argv[0]);
            exit(EXIT_FAILURE);
        }
    }

    printf("flags=%d; tfnd=%d; optind=%d\\n", flags, tfnd, optind);

    if (optind >= argc) {
        fprintf(stderr, "Expected argument after options\\n");
        exit(EXIT_FAILURE);
    }

    printf("name argument = %s\\n", argv[optind]);

    /* Other code omitted */

    exit(EXIT_SUCCESS);
}
.fi
.PP
The following example program illustrates the use of
.BR getopt_long ()
with most of its features.
.nf
.sp
#include <stdio.h>     /* for printf */
#include <stdlib.h>    /* for exit */
#include <getopt.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, \(aqc\(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("\\n");
            break;

        case \(aq0\(aq:
        case \(aq1\(aq:
        case \(aq2\(aq:
            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 \(aqa\(aq:
            printf("option a\\n");
            break;

        case \(aqb\(aq:
            printf("option b\\n");
            break;

        case \(aqc\(aq:
            printf("option c with value \(aq%s\(aq\\n", optarg);
            break;

        case \(aqd\(aq:
            printf("option d with value \(aq%s\(aq\\n", optarg);
            break;

        case \(aq?\(aq:
            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(EXIT_SUCCESS);
}
.fi
.SH SEE ALSO
.BR getsubopt (3)