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.