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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 as-
       signing  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 un-
       known 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.