"Also it is huge file so i cannot use array or hash."

How huge?
Have you tried it with a hash - you might be surprised :)

Update: Note - as correctly pointed out by chrism01, the below won't work where you have odd numbers of duplicates. See below for a solution that I believe addresses that issue.

Give the following a go: 

#!/usr/bin/perl -w
use strict;

my %wanted;

while (<DATA>) {
    exists $wanted{$_} ? delete $wanted{$_} : $wanted{$_}++;
}

print sort keys %wanted;

__DATA__
a1a
a1a
b1b
c1c
c1c
d1d
d1d
e1e
f1f
g1g
g1g
h1h
h1h
i1i
j1j

[download]
Output: 
b1b
e1e
f1f
i1i
j1j

[download]

Update: or as a one-liner: 

 perl -ne 'exists $x{$_}?delete $x{$_}:$x{$_}++;}{print for sort keys 
+%x;' < input.txt > output.txt

[download]

Try running that on your input file. The point about using a hash in that way is that you are only creating hash keys for those lines that are unique (and only appear once), so it's actually quite efficient. Whenever you are thinking "unique", a hash is almost certainly what you want.

Cheers,
Darren :)

In reply to Re: Read file line by line and check equal lines by McDarren
in thread Read file line by line and check equal lines by Anonymous Monk

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