__HASH__

$VAR1 = {
'Key1' => 'Cat.Mouse.Game.Lion.Tiger.Elephant',
'Key2' => 'Cat.Mouse.Game.Lion.Tiger.Lion',
'Key3' => 'Cat.Mouse.Game.Lion.Tiger.Monkey',
};

##</code><code>##

__DATA__

Pigeon.Lion.Tiger.Elephant SOME_DATA
Pigeon.Lion.Tiger.Lion SOME_DATA
Pigeon.Lion.Tiger.Monkey SOME_DATA

##</code><code>##

__Example code__

my %hash = ()
my $file = 'master.txt';
open (my $OUT_FILE, '<', "TEXT_FILE") or die "ERROR";

while (<$OUT_FILE>)  {   
    print "$. \n" if /SOME_DATA/; #searching SOME_DATA and printing
}


##</code><code>##

__OUTPUT__

Pigeon.Lion.Tiger.Elephant SOME_DATA (Key1)
Pigeon.Lion.Tiger.Monkey SOME_DATA (Key3)