int getopt(argc, argv, optstring)
int argc;
char **argv;
char *optstring;
extern char *optarg;
extern int optind;
extern int opterr;
 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.

On return from
 getopt , optarg is set to point to the start of any option argument.
 Optind contains the
 argv index of the next argument to be processed.

 Opterr and
 optind are both initialized to 1.
In order to use
 getopt to evaluate multiple sets of arguments, or to evaluate a single set of
arguments multiple times,
 optind must be initialized to the number of argv entries to be skipped in each
evaluation.

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 the ``--'' 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 , or it encounters an option that requires an argument which is not
supplied.
Setting
 opterr to a zero will disable these error messages.
 EXAMPLE
extern char *optarg;
extern int optind;
int bflag, ch, fd;

bflag = 0;
while ((ch = getopt(argc, argv, "bf:")) != EOF)
 switch(ch) {
 case 'b':
 bflag = 1;
 break;
 case 'f':
 if ((fd = open(optarg, O_RDONLY, 0)) < 0) {
 (void)fprintf(stderr,
 "myname: unable to read file %s.\en", optarg);
 exit(1);
 }
 break;
 case '?':
 default:
 usage();
 }
argc -= optind;
argv += optind;

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

A single dash (``-'') may be specified as an character in
 optstring , however it should
 never have an argument associated with it.
This allows
 getopt to be used with programs that expect ``-'' as an option flag.
This practice is wrong, and should not be used in any current development.
It is provided for backward compatibility
 only . By default, a single dash causes
 getopt to return EOF.
This is, we believe, compatible with System V.

It is also possible to handle digits as option letters.
This allows
 getopt to be used with programs that expect a number (``-3'') as an option.
This practice is wrong, and should not be used in any current development.
It is provided for backward compatibility
 only . The following code fragment works fairly well.
int length;
char *p;

while ((c = getopt(argc, argv, "0123456789")) != EOF)
 switch (c) {
 case '0': case '1': case '2': case '3': case '4':
 case '5': case '6': case '7': case '8': case '9':
 p = argv[optind - 1];
 if (p[0] == '-' && p[1] == ch && !p[2])
 length = atoi(++p);
 else
 length = atoi(argv[optind] + 1);
 break;
 }
}