while  ( $string =~ /((?:A|B)\d{3})/g ) {
  if ( $1 eq 'A000' or 
       ( $1 ge 'A123' and $1 le 'A456' ) or
       ( $1 ge 'A999' and $1 le 'B000' ) or
       ( $1 ge 'B789' and $1 le 'B888' )
      ) {
	 print "$1 matched\n";
       }
  else { print "$1 did not match\n" }