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GETOPT(3)		  OpenBSD Programmer's Manual		     GETOPT(3)

NAME
     getopt - get option character from command line argument list

SYNOPSIS
     #include <unistd.h>

     extern char *optarg;
     extern int opterr;
     extern int optind;
     extern int optopt;
     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, characters followed by a colon, and characters
     followed by two colons.  A character followed by a single colon indicates
     that an argument is to follow the option on the command line.  Two colons
     indicates that the argument is optional - this is an extension not
     covered by POSIX.	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; except in the case where the argument is optional,
     denoted with two colons, no leading whitespace is permitted.

     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 variables opterr and optind are both initialized to 1.	 The optind
     variable may be set to another value larger than 0 before a set of calls
     to getopt() in order to skip over more or less argv entries.  An optind
     value of 0 is reserved for compatibility with GNU getopt().

     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.

ENVIRONMENT
     POSIXLY_CORRECT	If set, a leading `-' in optstring is ignored.

EXAMPLES
     The following code accepts the options -b and -f argument and adjusts
     argc and argv after option argument processing has completed.

	   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)) == -1)
				   err(1, "%s", optarg);
			   break;
		   default:
			   usage();
			   /* NOTREACHED */
		   }
	   }
	   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 getopt() function implements a superset of the functionality
     specified by IEEE Std 1003.1 (``POSIX'').

     The following extensions are supported:

     o	  The optreset variable was added to make it possible to call the
	  getopt() function multiple times.

     o	  If the optind variable is set to 0, getopt() will behave as if the
	  optreset variable has been set.  This is for compatibility with GNU
	  getopt().  New code should use optreset instead.

     o	  If the first character of optstring is a plus sign (`+'), it will be
	  ignored.  This is for compatibility with GNU getopt().

     o	  If the first character of optstring is a dash (`-'), non-options
	  will be returned as arguments to the option character `\1'.  This is
	  for compatibility with GNU getopt().

     o	  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() semantics
	  (see above).	By default, a single dash causes getopt() to return
	  -1.

     Historic BSD versions of getopt() set optopt to the last option character
     processed.	 However, this conflicts with IEEE Std 1003.1 (``POSIX'')
     which stipulates that optopt be set to the last character that caused an
     error.

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>.

     It is 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 and can handle mixed number
     and letter arguments.

	   int aflag = 0, bflag = 0, ch, lastch = '\0';
	   int length = -1, newarg = 1, prevoptind = 1;

	   while ((ch = getopt(argc, argv, "0123456789ab")) != -1) {
		   switch (ch) {
		   case '0': case '1': case '2': case '3': case '4':
		   case '5': case '6': case '7': case '8': case '9':
			   if (newarg || !isdigit(lastch))
				   length = 0;
			   else if (length > INT_MAX / 10)
				   usage();
			   length = (length * 10) + (ch - '0');
			   break;
		   case 'a':
			   aflag = 1;
			   break;
		   case 'b':
			   bflag = 1;
			   break;
		   default:
			   usage();
		   }
		   lastch = ch;
		   newarg = optind != prevoptind;
		   prevoptind = optind;
	   }

OpenBSD 4.9			April 12, 2009			   OpenBSD 4.9
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