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NetBSD 6.1.5 - man page for getopt (netbsd section 3)

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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 character 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.  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 whitespace.

     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 processed (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
     extern char *optarg;
     extern int optind;
     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\n", 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 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
     development.  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 sin-
     gle 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;

	   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';
			   else
				   length = strtol(argv[optind] + 1, NULL, 10);
			   break;
		   }
	   }

BSD					September 10, 2003				      BSD
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