Random Walk is quite right... This is just to further demonstrate the case where the file is too big to hold in memory.

If each of your 'blocks' begin with an @:1107532976::1-like pattern, and each of those are expected to be unique, then just focus on the lines that contain that pattern:

use strict;
use warnings;

my %entries = ();
while (<DATA>) {
    chomp;
    if (/^\@:\d+/) { #if line starts with aht-colon-digit(s)
        if (exists $entries{$_}) { #$_ is the current line
            #$. is the current line number
            print "Line $. duplicates line $entries{$_} [$_]\n"; 
        }
        else
        {
            $entries{$_} = $.;
        }
    } 
}
1;
__DATA__
@:1107530184::1
kkkkkkkkkkkkmkmkmk
kkkkkk
confused.gif
@:1107530257:1107530439:1
kmkmkm
<br>kmkmkm
<br>
<br>Fri Feb  4 10:17:37 2005
<br>
mad.gif
@:1107530709::1
ygyg
ygygygyg
lol.gif
@:1107530717::1
ygyg
ygygygyg
lol.gif
@:1107530963::1
cool
help
cool.gif
@:1107532649:1107532689:1
k
<br>kkkkkkkkkkkkkkkkk
<br>
<br>Fri Feb  4 10:57:29 2005
<br>
lol
lol.gif
@:1107530257:1107530439:1
kmkmkm
<br>kmkmkm
<br>
<br>Fri Feb  4 10:17:37 2005
<br>
mad.gif
@:1107532758::1
lll
Lets
mad.gif
@:1107532976::1
lll
Lets
mad.gif

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Hanlon's Razor - "Never attribute to malice that which can be adequately explained by stupidity"

In reply to Re^2: Regular Expression to find duplicate text blocks by Art_XIV
in thread Regular Expression to find duplicate text blocks by Anonymous Monk

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