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 (this  is  disabled  by  the  POSIX_BUILTINS  option).
       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.
