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GETOPT(3)              FreeBSD 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 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 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
     #include <unistd.h>
     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 the 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 single
     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, *ep;

           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';
                                   ep = "";
                           } else if (argv[optind] && argv[optind][1] == ch) {
                                   length = strtol((p = argv[optind] + 1),
                                       &ep, 10);
                                   optind++;
                                   optreset = 1;
                           } else
                                   usage();
                           if (*ep != '\0')
                                   errx(EX_USAGE, "illegal number -- %s", p);
                           break;
                   }

FreeBSD 11.0-PRERELEASE         April 27, 1995         FreeBSD 11.0-PRERELEASE

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | EXAMPLES | DIAGNOSTICS | SEE ALSO | STANDARDS | HISTORY | BUGS

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