getopts optstring name [ arg ... ]
          Checks arg for legal options.  If arg is  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.  opt-
          string contains the letters  that  getopts  recognizes.
          If  a  letter  is  followed  by  a  `:', that option is
          expected to have  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.

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