Example

     The following example shows how you might process the arguments
     for a utility that can take the mutually exclusive options a
     and b and the options f and o, both of which require arguments:

#include <unistd.h>

int main (int argc, char *argv[ ])
{
         int c;
         int bflg, aflg, errflg;
         char *ifile;
         char *ofile;
         extern char *optarg;
         extern int optind, optopt;
         .
         .
         .
         while ((c = getopt(argc, argv, ":abf:o:)) != -1) {

                switch (c) {
                case 'a':
                        if (bflg)
                                errflg++;
                        else
                                aflg++;
                        break;
                case 'b':
                        if (aflg)
                               errflg++;
                        else {
                               bflg++;
                               bproc();
                        }

                        break;
                case 'f':
                        ifile = optarg;
                        break;
                case 'o':
                        ofile = optarg;
                        break;
                case ':':      /* -f or -o without operand */
                        fprintf (stderr,
                         "Option -%c requires an operand\n"' optopt);
                        errflg++;
                        break;
                case '?':
                        fprintf (stderr,
                                "Unrecognized option -%c\n"' optopt);
                        errflg++;
                }
         }
         if (errflg) {
                fprintf (stderr, "usage: ...");
                exit(2);
         }
         for ( ; optind < argc; optind++)  {
                if (access(argv[optind], R_OK)) {
         .
         .
         .
}

     This sample code accepts any of the following as equivalent:

       cmd -ao arg path path
       cmd -a -o arg path path
       cmd -o arg -a path path
       cmd -a -o arg -- path path
       cmd -a -oarg path path
       cmd -aoarg path path