gno/usr.man/man3/getopt.3

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.\"     @(#)getopt.3	8.4 (Berkeley) 4/19/94
.\"
.TH GETOPT 3 "26 January 1997" GNO "Library Routines"
.SH NAME
.BR getopt
\- get option character from command line argument list
.SH SYNOPSIS
#include <stdlib.h>
.sp 1
extern char *\fBoptarg\fR;
.br
extern int   \fBoptind\fR;
.br
extern int   \fBoptopt\fR;
.br
extern int   \fBopterr\fR;
.br
extern int   \fBoptreset\fR;
.sp 1
int
\fBgetopt\fR (int \fIargc\fR, char * const *\fIargv\fR, 
const char *\fIoptstring\fR);
.br
int \fBgetopt_restart\fR (void);
.SH DESCRIPTION
This manual page describes the BSD implementation of 
.BR getopt .
.LP
The
.BR getopt 
function incrementally parses a command line argument list
.I argv
and returns the next
.IR known 
option character.
An option character is
.IR known 
if it has been specified in the string of accepted option characters,
.IR optstring .
.LP
The option string
.I optstring
may contain the following elements: individual characters, and
characters followed by a colon to indicate an option argument
is to follow.
For example, an option string
.IR x
recognizes an option
.BR -x ,
and an option string
.BR x:
recognizes an option and argument
.BR "-x argument" .
It does not matter to
.BR getopt 
if a following argument has leading white space.
.LP
On return from
.BR getopt ,
.IR optarg
points to an option argument, if it is anticipated,
and the variable
.IR optind
contains the index to the next
.I argv
argument for a subsequent call
to
.BR getopt .
The variable
.IR optopt
saves the last
.IR known 
option character returned by
.BR getopt .
.LP
The variable
.IR opterr
and
.IR optind
are both initialized to 1.
The
.IR optind
variable may be set to another value before a set of calls to
.BR getopt 
in order to skip over more or less argv entries.
.LP
In order to use
.BR getopt 
to evaluate multiple sets of arguments, or to evaluate a single set of
arguments multiple times,
the variable
.IR optreset
must be set to 1 before the second and each additional set of calls to
.BR getopt ,
and the variable
.IR optind
must be reinitialized.
.LP
The
.BR getopt 
function
returns an
.BR EOF
when the argument list is exhausted, or a non-recognized
option is encountered.
The interpretation of options in the argument list may be canceled
by the option
.BR "--"
(double dash) which causes
.BR getopt 
to signal the end of argument processing and return an
.BR EOF . 
When all options have been processed (i.e., up to the first non-option
argument),
.BR getopt 
returns
.BR EOF .
.LP
The
.BR getopt_restart
function sets
.BR optreset
and
.BR optind
to 1 and returns zero.  It is provided for backwards compatibility
with older versions of GNO, and should be avoided in new code.
.SH DIAGNOSTICS
If the
.BR getopt 
function encounters a character not found in the string
.IR optarg
or detects
a missing option argument it writes an error message and returns
.BR ?
to the
.IR stderr .
Setting
.IR opterr
to a zero will disable these error messages.
If
.IR optstring 
has a leading 
.BR \&:
then a missing option argument causes a
.BR \&:
to be returned in addition to suppressing any error messages.
.LP
Option arguments are allowed to begin with
.BR \- ;
this is reasonable but
reduces the amount of error checking possible.
.SH EXTENSIONS
The
.IR optreset
variable was added to make it possible to call the
.BR getopt 
function multiple times.
This is an extension to the POSIX 1003.2 specification.
.LP
The
.BR getopt_reset
function is also an extension, but one that has been deprecated.
.SH LIMITATIONS
This implementation of
.BR getopt
does not allow one to mix options and non-option arguments; option
processing will halt as soon as the first non-option argument is
found.  The GNU implementation does not have this limitation, but also
cannot be restarted.  The GNU implementation also allows "long options",
where the option name may be more than one character.
.LP
See the GNO FAQ regarding availability of the GNU implementation of
.BR getopt
and 
.BR getopt_long (3)
for GNO.
.SH EXAMPLE
.nf
extern char *optarg;
extern int optind;
int bflag, ch, fd;

bflag = 0;
while ((ch = getopt(argc, argv, "bf:")) != EOF)
	switch(ch) {
	case 'b':
		bflag = 1;
		break;
	case 'f':
		if ((fd = open(optarg, O_RDONLY, 0)) < 0) {
			(void)fprintf(stderr,
			    "myname: %s: %s\en", optarg, strerror(errno));
			exit(1);
		}
		break;
	case '?':
	default:
		usage();
}
argc -= optind;
argv += optind;
.fi
.SH HISTORY
The
.BR getopt 
function appeared 4.3BSD.
.SH BUGS
A single dash
.BR \-
may be specified as an character in
.IR optstring ,
however it should
.IR never 
have an argument associated with it.
This allows
.BR getopt 
to be used with programs that expect
.BR \-
as an option flag.
This practice is wrong, and should not be used in any current development.
It is provided for backward compatibility
.IR only .
By default, a single dash causes
.BR getopt 
to return
.BR EOF .
This is, we believe, compatible with System V.
.LP
It is also possible to handle digits as option letters.
This allows
.BR getopt 
to be used with programs that expect a number (such as
.BR \-3 )
as an option.
This practice is wrong, and should not be used in any current development.
It is provided for backward compatibility
.IR only .
The following code fragment works in most cases.
.nf
int length;
char *p;

while ((c = getopt(argc, argv, "0123456789")) != EOF)
	switch (c) {
	case '0': case '1': case '2': case '3': case '4':
	case '5': case '6': case '7': case '8': case '9':
		p = argv[optind - 1];
		if (p[0] == '-' && p[1] == ch && !p[2])
			length = atoi(++p);
		else
			length = atoi(argv[optind] + 1);
		break;
	}
}
.fi
.SH SEE ALSO
.BR getsubopt (3),
.BR getopt_long (3G).