getopt(3C)      UNIX System V(C Programming Language Utilities)      getopt(3C)


NAME
      getopt - get option letter from argument vector

SYNOPSIS
      #include <stdlib.h>

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

      extern char *optarg;

      extern int optind, opterr, optopt;

DESCRIPTION
      getopt returns the next option letter in argv that matches a letter in
      optstring.  It supports all the rules of the command syntax standard [see
      intro(1)].  Since all new commands are intended to adhere to the command
      syntax standard, they should use getopts(1), getopt(3C), or
      getsubopts(3C) to parse positional parameters and check for options that
      are legal for that command.

      optstring must contain the option letters the command using getopt will
      recognize; if a letter is followed by a colon, the option is expected to
      have an argument, or group of arguments, which may be separated from it
      by white space.  optarg is set to point to the start of the option
      argument on return from getopt.

      getopt places in optind the argv index of the next argument to be
      processed.  optind is external and is initialized to 1 before the first
      call to getopt.  When all options have been processed (i.e., up to the
      first non-option argument), getopt returns EOF.  The special option
      ``--'' (two hyphens) may be used to delimit the end of the options; when
      it is encountered, EOF is returned and ``--'' is skipped. This is useful
      in delimiting non-option arguments that begin with ``-'' (hyphen).

EXAMPLE
      The following code fragment shows how one might process the arguments for
      a command that can take the mutually exclusive options a and b, and the
      option o, which requires an argument:

      #include <stdlib.h>
      #include <stdio.h>

      main (int argc, char **argv)
      {
            int c;
            extern char *optarg;
            extern int optind;
            int aflg = 0;
            int bflg = 0;
            int errflg = 0;
            char *ofile = NULL;



10/89                                                                    Page 1

getopt(3C)      UNIX System V(C Programming Language Utilities)      getopt(3C)


            while ((c = getopt(argc, argv, "abo:")) != EOF)
                  switch (c) {
                  case 'a':
                        if (bflg)
                              errflg++;
                        else
                              aflg++;
                        break;
                  case 'b':
                        if (aflg)
                              errflg++;
                        else
                              bflg++;
                        break;
                  case 'o':
                        ofile = optarg;
                        (void)printf("ofile = %s\n", ofile);
                        break;
                  case '?':
                        errflg++;
                  }
            if (errflg) {
                  (void)fprintf(stderr,
                        "usage: cmd [-a|-b] [-o<file>] files...\n");
                  exit (2);
            }
            for ( ; optind < argc; optind++)
                  (void)printf("%s\n", argv[optind]);
            return 0;
      }

SEE ALSO
      getsubopt(3C).
      getopts(1), intro(1) in the User's Reference Manual.

DIAGNOSTICS
      getopt prints an error message on the standard error and returns a ``?''
      (question mark) when it encounters an option letter not included in
      optstring or no argument after an option that expects one.  This error
      message may be disabled by setting opterr to 0.  The value of the
      character that caused the error is in optopt.

NOTES
      The library routine getopt does not fully check for mandatory arguments.
      That is, given an option string a:b and the input -a -b, getopt assumes
      that -b is the mandatory argument to the option -a and not that -a is
      missing a mandatory argument.

      It is a violation of the command syntax standard [see intro(1)] for
      options with arguments to be grouped with other options, as in cmd
      -aboxxx file, where a and b are options, o is an option that requires an
      argument, and xxx is the argument to o.  Although this syntax is


Page 2                                                                    10/89

getopt(3C)      UNIX System V(C Programming Language Utilities)      getopt(3C)


      permitted in the current implementation, it should not be used because it
      may not be supported in future releases. The correct syntax is cmd -ab
      -oxxx file.



















































10/89                                                                    Page 3