.Delete all lines contained a string.
      At first exclude lines containing the string by EXClude command,
      then use DROp X ALL command
      To delete all lines not include the string,use DROP NX ALL.
      To display all lines containing the string use FINd cmd
      after excluded all line by "x all" cmd.
      To select the line range around the line containing search word,
      use -a and/or -b option.
      use XX cmd to exchange displayed and excluded lines.