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.\"     @(#)getopt.3	8.4.1 (2.11BSD) 1996/1/12
.\"
.TH GETOPT 3 "January 12, 1996"
.UC 6
.SH NAME
\fBgetopt\fP \- get option character from command line argument list
.SH SYNOPSIS
.B #include <stdlib.h>
.sp
.B extern char *optarg;
.br
.B extern int   optind;
.br
.B extern int   optopt;
.br
.B extern int   opterr;
.br
.B extern int   optreset;
.sp
.I int
.br
\fBgetopt\fP(argc, argv, optstring)
.br
.I int argc;
.br
.I char **argv;
.br
.I char *optstring;
.SH DESCRIPTION
The
.BR getopt ()
function incrementally parses a command line argument list
.I argv
and returns the next
.I known
option character.
An option character is
.I known
if it has been specified in the string of accepted option characters,
.IR optstring .
.PP
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
"\&""x""
recognizes an option
``\-\fBx\fP'',
and an option string
"\&""x:""
recognizes an option and argument
``\fB\-x\fP \fIargument\fP''.
It does not matter to
.BR getopt ()
if a following argument has leading white space.
.PP
On return from
.BR getopt (),
.I optarg
points to an option argument, if it is anticipated,
and the variable
.I optind
contains the index to the next
.I argv
argument for a subsequent call
to
.BR getopt ().
The variable
.I optopt
saves the last
.I known
option character returned by
.BR getopt ().
.PP
The variable
.I opterr
and
.I optind
are both initialized to 1.
The
.I 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.
.PP
In order to use
.BR getopt ()
to evaluate multiple sets of arguments, or to evaluate a single set of
arguments multiple times,
the variable
.I optreset
must be set to 1 before the second and each additional set of calls to
.BR getopt (),
and the variable
.I optind
must be reinitialized.
.PP
The
.BR getopt ()
function
returns an
.B EOF
when the argument list is exhausted, or a non-recognized
option is encountered.
The interpretation of options in the argument list may be cancelled
by the option `\-\-'
(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 .
.SH DIAGNOSTICS
If the
.BR getopt ()
function encounters a character not found in the string
.I optarg
or detects
a missing option argument it writes an error message and returns `?'
to the
.IR stderr .
Setting
.I opterr
to a zero will disable these error messages.
If
.I optstring 
has a leading 
`\&:'
then a missing option argument causes a
`\&:'
to be returned in addition to suppressing any error messages.
.PP
Option arguments are allowed to begin with
`\-';
this is reasonable but
reduces the amount of error checking possible.
.SH EXTENSIONS
The
.I optreset
variable was added to make it possible to call the
.BR getopt ()
function multiple times.
This is an extension to the
IEEE Std1003.2 (``POSIX'')
specification.
.SH EXAMPLE
.nf
.cs R 24
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;
.br
.cs R
.fi
.SH HISTORY
The
.BR getopt ()
function appeared 4.3BSD.
.SH BUGS
A single dash ``\-''
may be specified as an character in
.I optstring ,
however it should
.B never
have an argument associated with it.
This allows
.BR getopt ()
to be used with programs that expect
``\-''
as an option flag.
This practice is wrong, and should not be used in any current development.
It is provided for backward compatibility
.B only .
By default, a single dash causes
.BR getopt ()
to return
.BR EOF .
This is, we believe, compatible with System V.
.PP
It is also possible to handle digits as option letters.
This allows
.BR getopt ()
to be used with programs that expect a number
(``-3'')
as an option.
This practice is wrong, and should not be used in any current development.
It is provided for backward compatibility
.BR only .
The following code fragment works in most cases.
.sp
.nf
.cs R 24
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;
	}
}
.cs R