open( IP_FH, "test.txt" );

while (<IP_FH>) {
    if ( /ABCD/ ... /EFGH/ ) {
        $match = 1;
        $found  .= $_;
    }
    else {
      if ( $match ) {
          $match = 0  ;
          print "========\n";
          print $found;
          $found = ();
      }
   }
}