getopt(3) - NetBSD Manual Pages

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GETOPT(3)                 NetBSD Programmer's 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 charac-
     ters, optstring.

     The option string optstring may contain the following elements: individu-
     al 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 argu-
     ment ``-x argument''.  It does not matter to getopt() if a following ar-
     gument 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 -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 returns -1.  When all options have been processed
     (i.e., up to the first non-option argument), getopt() returns -1.


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 ar-
     gument 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 Std 1003.2
     (``POSIX.2'') specification.


EXAMPLE

     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;


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 develop-
     ment.  It is provided for backward compatibility only.  By default, a
     single dash causes getopt() to return -1.  This is, we believe, compati-
     ble 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 op-
     tion.  This practice is wrong, and should not be used in any current de-
     velopment.  It is provided for backward compatibility only.  The follow-
     ing code fragment works in most cases.

           int length;
           char *p;

           while ((c = getopt(argc, argv, "0123456789")) != -1)
                   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;
                   }
           }

NetBSD 1.5                      April 27, 1995                               2