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.\"	@(#)getopt.3	6.11 (Berkeley) %G%
.\"
.TH GETOPT 3 ""
.UC 6
.SH NAME
getopt \- get option letter from argv
.SH SYNOPSIS
.ft B
int getopt(argc, argv, optstring)
.br
int argc;
.br
char **argv;
.br
char *optstring;
.sp
extern char *optarg;
.br
extern int optind;
.br
extern int opterr;
.ft
.SH DESCRIPTION
.I Getopt
returns the next option letter in
.I argv
that matches a letter in
.IR optstring .
.I Optstring
is a string of recognized option letters;
if a letter is followed by a colon, the option is expected to have
an argument that may or may not be separated from it by white space.
.I Optarg
is set to point to the start of the option argument on return from
.IR getopt .
.PP
.I Getopt
places in
.I optind
the
.I argv
index of the next argument to be processed.
Because
.I optind
is external, it is normally initialized to zero automatically
before the first call to 
.IR getopt .
.PP
When all options have been processed (i.e., up to the first
non-option argument),
.I getopt
returns
.BR EOF .
The special option
.B \-\-
may be used to delimit the end of the options;
.B EOF
will be returned, and
.B \-\-
will be skipped.
.SH DIAGNOSTICS
.I Getopt
prints an error message on
.I stderr
and returns a question mark
.RB ( ? )
when it encounters an option letter not included in
.IR optstring .
Setting \fIopterr\fP to a zero will disable this error message.
.SH EXAMPLE
The following code fragment shows how one might process the arguments
for a command that can take the mutually exclusive options
.B a
and
.BR b ,
and the options
.B f
and
.BR o ,
both of which require arguments:
.PP
.RS
.nf
main(argc, argv)
int argc;
char **argv;
{
	int c;
	extern int optind;
	extern char *optarg;
	\&.
	\&.
	\&.
	while ((c = getopt(argc, argv, "abf:o:")) != EOF)
		switch (c) {
		case `a':
			if (bflg)
				errflg++;
			else
				aflg++;
			break;
		case `b':
			if (aflg)
				errflg++;
			else
				bproc();
			break;
		case `f':
			ifile = optarg;
			break;
		case `o':
			ofile = optarg;
			break;
		case `?':
		default:
			errflg++;
			break;
		}
	if (errflg) {
		fprintf(stderr, "Usage: ...");
		exit(2);
	}
	for (; optind < argc; optind++) {
		\&.
		\&.
		\&.
	}
	\&.
	\&.
	\&.
}
.RE
.SH HISTORY
Written by Henry Spencer, working from a Bell Labs manual page.
.SH BUGS
``-'' may be specified as an option letter, however it should never
have an argument associated with it.  This allows \fIgetopt\fP 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 \fBonly\fP.
.PP
It is possible to handle digits as option letters.  This allows
\fIgetopt\fP 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
\fBonly\fP.  The following code fragment, while not perfect, works
fairly well.
.RS
.nf

	int minlen;
	char *p;

	minlen = -1;
	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':
			if (minlen == -1) {
				p = argv[optind - 1];
				if (p[0] == '-' && p[1] == ch && !p[2])
					minlen = atoi(++p);
				else
					minlen = atoi(argv[optind] + 1);
			}
			break;
		}
	}
	\&.
	\&.
	\&.
.RE
.fi
.PP
Option arguments are allowed to begin with ``\-'';
this is reasonable but reduces the amount of error checking possible.
.PP
.I Getopt
is quite flexible but the obvious price must be paid:  there is much
it could do that it doesn't, like
checking mutually exclusive options, checking type of
option arguments, etc.