GETOPT(3)                                                            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
       _G_e_t_o_p_t  returns the next option letter in _a_r_g_v that matches a letter in
       _o_p_t_s_t_r_i_n_g.  _O_p_t_s_t_r_i_n_g is a string of recognized option  letters;  if  a
       letter  is followed by a colon, the option is expected to have an argu‐
       ment that may or may not be separated from it by white  space.   _O_p_t_a_r_g
       is  set  to  point  to  the start of the option argument on return from
       _g_e_t_o_p_t.

       _G_e_t_o_p_t places in _o_p_t_i_n_d the _a_r_g_v index of the next argument to be  pro‐
       cessed.  Because _o_p_t_i_n_d is external, it is normally initialized to zero
       automatically before the first call to _g_e_t_o_p_t.

       When all options have been processed (i.e., up to the first  non-option
       argument),  _g_e_t_o_p_t  returns  EOF.  The special option -- may be used to
       delimit the end of the options; EOF will be returned, and  --  will  be
       skipped.

DIAGNOSTICS
       _G_e_t_o_p_t  prints  an  error message on _s_t_d_e_r_r and returns a question mark
       (?)  when it encounters an option letter not included in _o_p_t_s_t_r_i_n_g.

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.   Modi‐
       fied by Keith Bostic to behave more like the System V version.

BUGS
       It  is not obvious how ‘-’ standing alone should be treated;  this ver‐
       sion 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.

       _G_e_t_o_p_t  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.



4.3 Berkeley Distribution        May 27, 1986                        GETOPT(3)