x                  The next option character specified on the
                       command line.

                       A colon is returned if getopt detects a
                       missing argument and the first character of
                       optstring is a colon.

                       A question mark is returned if getopt
                       encounters an option character not in
                       optstring or detects a missing argument and
                       the first character of optstring is not a
                       colon.
    -1                 When all command-line options are parsed.