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

NAME

     getopt -- get option character from command line argument list

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <unistd.h>

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

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

DESCRIPTION

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

     The option string optstring may contain the following elements: individual characters, and characters followed by a colon to indicate an
     option argument is to follow.  If an individual character is followed by two colons, then the option argument is optional; optarg is set to
     the rest of the current argv word, or NULL if there were no more characters in the current word.  This is a GNU extension.  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 mat-
     ter 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 variables 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.  The interpretation of options 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 pro-
     cessed (i.e., up to the first non-option argument), getopt() returns -1.

RETURN VALUES

     The getopt() function returns the next known option character in optstring.  If getopt() encounters a character not found in optstring or if
     it detects a missing option argument, it returns '?' (question mark).  If optstring has a leading ':' then a missing option argument causes
     ':' to be returned instead of '?'.  In either case, the variable optopt is set to the character that caused the error.  The getopt() function
     returns -1 when the argument list is exhausted.

EXAMPLES

     #include <unistd.h>
     int bflag, ch, fd;

     bflag = 0;
     while ((ch = getopt(argc, argv, "bf:")) != -1) {
	     switch (ch) {
	     case 'b':
		     bflag = 1;
		     break;
	     case 'f':
		     if ((fd = open(optarg, O_RDONLY, 0)) < 0) {
			     (void)fprintf(stderr,
				 "myname: %s: %s
", optarg, strerror(errno));
			     exit(1);
		     }
		     break;
	     case '?':
	     default:
		     usage();
	     }
     }
     argc -= optind;
     argv += optind;

DIAGNOSTICS

     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 option 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.

SEE ALSO

     getopt(1), getopt_long(3), getsubopt(3)

STANDARDS

     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.

HISTORY

     The getopt() function appeared in 4.3BSD.

BUGS

     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 devel-
     opment.  It is provided for backward compatibility only.  Care should be taken not to use '-' as the first character in optstring to avoid a
     semantic conflict with GNU getopt(), which assigns different meaning to an optstring that begins with a '-'.  By default, a single dash
     causes getopt() to return -1.

     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
     option.  This practice is wrong, and should not be used in any current development.  It is provided for backward compatibility only.  The
     following code fragment works in most cases.

	   int ch;
	   long 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 = ch - '0';
				   ep = "";
			   } else if (argv[optind] && argv[optind][1] == ch) {
				   length = strtol((p = argv[optind] + 1),
				       &ep, 10);
				   optind++;
				   optreset = 1;
			   } else
				   usage();
			   if (*ep != '')
				   errx(EX_USAGE, "illegal number -- %s", p);
			   break;
		   }

BSD
								   June 5, 2014 							       BSD