MirOS Manual: getopt(3)

GETOPT(3)                  BSD 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 charac-
     ters, optstring.

     The option string optstring may contain the following elements: individu-
     al characters, characters followed by a colon, and characters followed by
     two colons. A character followed by a single colon indicates that an ar-
     gument is to follow the option on the command line. Two colons indicates
     that the argument is optional - this is an extension not covered by PO-
     SIX. 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 ar-
     gument 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

     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 mes-
     sage to 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.

SEE ALSO

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

STANDARDS

     The getopt() function implements a superset of the functionality speci-
     fied 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 op-
          tion 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;
           }

MirOS BSD #10-current          December 4, 2011                              2

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