getopt(3) — bsd

GETOPT(3)                            BSD                             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 (that is, 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.

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++) {
                    .
                    .
                    .
               }
               .
               .
               .
          }

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

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.

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