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GETOPT(3)		 BSD Library Functions Manual		     GETOPT(3)

     getopt -- get option character from command line argument list

     Standard C	Library	(libc, -lc)

     #include <unistd.h>

     extern char *optarg;
     extern int	optind;
     extern int	optopt;
     extern int	opterr;
     extern int	optreset;

     getopt(int	argc, char * const *argv, const	char *optstring);

     The getopt() function incrementally parses	a command line argument	list
     argv and returns the next known option character.	An option character is
     known if it has been specified in the string of accepted option charac-
     ters, optstring.

     The option	string optstring may contain the following elements: individ-
     ual characters, and characters followed by	a colon	to indicate an option
     argument is to follow.  For example, an option string "x" recognizes an
     option "-x", and an option	string "x:" recognizes an option and argument
     "-x argument".  It	does not matter	to getopt() if a following argument
     has leading white space.

     On	return from getopt(), optarg points to an option argument, if it is
     anticipated, and the variable optind contains the index to	the next argv
     argument for a subsequent call to getopt().  The variable optopt saves
     the last known option character returned by getopt().

     The variable opterr and optind are	both initialized to 1.	The optind
     variable may be set to another value before a set of calls	to getopt() in
     order to skip over	more or	less argv entries.

     In	order to use getopt() to evaluate multiple sets	of arguments, or to
     evaluate a	single set of arguments	multiple times,	the variable optreset
     must be set to 1 before the second	and each additional set	of calls to
     getopt(), and the variable	optind must be reinitialized.

     The getopt() function returns -1 when the argument	list is	exhausted, or
     `?' if a non-recognized option is encountered.  The interpretation	of op-
     tions in the argument list	may be cancelled by the	option `--' (double
     dash) which causes	getopt() to signal the end of argument processing and
     return -1.	 When all options have been processed (i.e., up	to the first
     non-option	argument), getopt() returns -1.

     If	the getopt() function encounters a character not found in the string
     optstring or detects a missing option argument it writes an error message
     to	the stderr and returns `?'.  Setting opterr to a zero will disable
     these error messages.  If optstring has a leading `:' then	a missing op-
     tion argument causes a `:'	to be returned in addition to suppressing any
     error messages.

     Option arguments are allowed to begin with	"-"; this is reasonable	but
     reduces the amount	of error checking possible.

     The optreset variable was added to	make it	possible to call the getopt()
     function multiple times.  This is an extension to the IEEE	Std 1003.2
     ("POSIX.2") specification.

     int bflag,	ch, fd;

     bflag = 0;
     while ((ch	= getopt(argc, argv, "bf:")) !=	-1)
	     switch (ch) {
	     case 'b':
		     bflag = 1;
	     case 'f':
		     if	((fd = open(optarg, O_RDONLY, 0)) < 0)
			     err(1, "%s", optarg);
	     case '?':
     argc -= optind;
     argv += optind;

     The getopt() function appeared in 4.3BSD.

     The getopt() function was once specified to return	EOF instead of -1.
     This was changed by IEEE Std 1003.2-1992 ("POSIX.2") to decouple getopt()
     from _stdio.h_.

     A single dash "-" may be specified	as a character in optstring, however
     it	should never have an argument associated with it.  This	allows
     getopt() to be used with programs that expect "-" as an option flag.
     This practice is wrong, and should	not be used in any current develop-
     ment.  It is provided for backward	compatibility only.  By	default, a
     single dash causes	getopt() to return -1.	This is, we believe, compati-
     ble with System V.

     It	is also	possible to handle digits as option letters.  This allows
     getopt() to be used with programs that expect a number ("-3") as an op-
     tion.  This practice is wrong, and	should not be used in any current de-
     velopment.	 It is provided	for backward compatibility only.  The follow-
     ing code fragment works in	most (but not all) cases.

	   int length;
	   char	*p, *ep;

	   while ((ch =	getopt(argc, argv, "0123456789")) != -1)
		   switch (ch) {
		   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 = strtol(++p,	&ep, 10);
			   else	if (argv[optind] && argv[optind][1] == ch) {
				   length = strtol((p =	argv[optind] + 1),
				       &ep, 10);
				   optreset = 1;
			   } else
			   if (*ep != '	')
				   errx(EX_USAGE, "illegal number -- %s", p);

BSD				April 27, 1995				   BSD


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