getopts optstring name [ arg ... ]
       Checks the args for legal options.  If the args are omitted, use
       the positional parameters.  A valid option argument begins with a
       `+' or a `-'.  An argument not beginning with a `+' or a `-', or
       the argument `--', ends the options.  Note that a single `-' is
       not considered a valid option argument.  optstring contains the
       letters that getopts recognizes.  If a letter is followed by a
       `:', that option requires an argument.  The options can be
       separated from the argument by blanks.

       Each time it is invoked, getopts places the option letter it finds
       in the shell parameter name, prepended with a `+' when arg begins
       with a `+'.  The index of the next arg is stored in OPTIND.  The
       option argument, if any, is stored in OPTARG.

       The first option to be examined may be changed by explicitly
       assigning to OPTIND.  OPTIND has an initial value of 1, and is
       normally set to 1 upon entry to a shell function and restored upon
       exit.  (The POSIX_BUILTINS option disables this, and also changes
       the way the value is calculated to match other shells.)  OPTARG is
       not reset and retains its value from the most recent call to
       getopts.  If either of OPTIND or OPTARG is explicitly unset, it
       remains unset, and the index or option argument is not stored.
       The option itself is still stored in name in this case.

       A leading `:' in optstring causes getopts to store the letter of
       any invalid option in OPTARG, and to set name to `?' for an
       unknown option and to `:' when a required argument is missing.
       Otherwise, getopts sets name to `?' and prints an error message
       when an option is invalid.  The exit status is nonzero when there
       are no more options.
