Here's one way: 
use warnings;
use strict;

my $string  = "ATATTTATATTAT";
my $removed = substr($string, 0, 3);
$string     = substr($string, 3);
print "$string $removed\n";

__END__

TTTATATTAT ATA

[download]

UPDATE: Fixed bug. Thanks AnomalousMonk

In reply to Re: Extract string after removing the substring by toolic
in thread Extract string after removing the substring by viktor

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