getopt(3)

NAME

     getopt - get option letter from argv

SYNOPSIS

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

     extern char *optarg;
     extern int optind;

DESCRIPTION

     Getopt returns the next option letter in argv that matches  a  letter  in
     optstring.   Optstring  is  a  string  of recognized option letters; if a
     letter is followed by a colon, the option is expected to have an argument
     that  may  or may not 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.   Because  optind  is  external, it is normally initialized to
     zero automatically 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 -- may be used to
     delimit the end of the options; EOF will be  returned,  and  --  will  be
     skipped.

DIAGNOSTICS

     Getopt prints an error message on stderr and returns a question mark  (?)
     when it encounters an option letter not included in optstring.

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
     options f and o, both of which require arguments:

          main(argc, argv)
          int argc;
          char **argv;
          {
                  int c;
                  extern int optind;
                  extern char *optarg;
                  .
                  .
                  .
                  while ((c = getopt(argc, argv, "abf:o:")) != EOF)
                          switch (c) {
                          case `a':
                                  if (bflg)
                                          errflg++;
                                  else
                                          aflg++;
                                  break;
                          case `b':
                                  if (aflg)
                                          errflg++;
                                  else
                                          bproc();
                                  break;
                          case `f':
                                  ifile = optarg;
                                  break;
                          case `o':
                                  ofile = optarg;
                                  break;
                          case `?':
                          default:
                                  errflg++;
                                  break;
                          }
                  if (errflg) {
                          fprintf(stderr, "Usage: ...");
                          exit(2);
                  }
                  for (; optind < argc; optind++) {
                          .
                          .
                          .
                  }
                  .
                  .
                  .
          }

HISTORY

     Written by Henry Spencer, working from a Bell Labs manual page.  Modified
     by Keith Bostic to behave more like the System V version.

BUGS

     It is not obvious how `-' standing alone should be treated;  this version
     treats it as a non-option argument, which is not always right.

     Option arguments are allowed to begin with `-'; this  is  reasonable  but
     reduces the amount of error checking possible.

     Getopt is quite flexible but the obvious price must be  paid:   there  is
     much  it  could  do  that  it  doesn't,  like checking mutually exclusive
     options, checking type of option arguments, etc.