Range Operators are handy for this...

use warnings;
use strict;

while (<DATA>) {
    print if /line X/ .. /Line Y/;
}

__DATA__
HLU Number     ALU Number
  ----------     ----------
    0               233   ==> line X
    1               234
    2               235
    3               236
    4               237
    5               238
    6               240
    7               239
    8               241
    9               243
    10              242
    11              244
    12              245
    13              246
    14              247
    15              263
    16              248
    17              249
    18              250
    19              251
    20              252
    21              253
    22              254
    23              255 ==> Line Y
Shareable:             YES
[download]

This is a FAQ:

perldoc -q between
[download]