bsd man page for getopt

GETOPT(3)						     Library Functions Manual							 GETOPT(3)

NAME
       getopt - get option character from command line argument list

SYNOPSIS
       #include <stdlib.h>

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

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

DESCRIPTION
       The  getopt() function incrementally parses a command line argument list argv and returns the next known option character.  An option char-
       acter 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 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 an EOF when the argument list is exhausted, or a non-recognized option is encountered.  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 process-
       ing and return an EOF.  When all options have been processed (i.e., up to the first non-option argument), getopt() returns EOF.

DIAGNOSTICS
       If the getopt() function encounters a character not found in the string optarg or detects a missing option argument it writes an error mes-
       sage and returns `?'  to the stderr.  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.

EXTENSIONS
       The  optreset  variable	was  added  to	make  it  possible to call the getopt() function multiple times.  This is an extension to the IEEE
       Std1003.2 (``POSIX'') specification.

EXAMPLE
       extern char *optarg;
       extern int optind;
       int bflag, ch, fd;

       bflag = 0;
       while ((ch = getopt(argc, argv, "bf:")) != EOF)
	    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;

HISTORY
       The getopt() function appeared 4.3BSD.

BUGS
       A single dash ``-'' may be specified as an 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 cur-
       rent development.  It is provided for backward compatibility only .  By default, a single dash causes getopt() to return EOF.  This is,	we
       believe, compatible 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
       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 length;
       char *p;

       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':
		 p = argv[optind - 1];
		 if (p[0] == '-' && p[1] == ch && !p[2])
		      length = atoi(++p);
		 else
		      length = atoi(argv[optind] + 1);
		 break;
	    }
       }

4.3 Berkeley Distribution					 January 12, 1996							 GETOPT(3)