oct('0'. NNN) converts octal string to decimal number.
pack('U', decimal code point) makes utf8 decoded character.

use strict;
use warnings;

my $str='\334ber@n\374ber.com';
$str =~ s/\\(\d{3})/pack('U', oct('0'.$1))/eg;

binmode STDOUT, ":encoding(UTF-8)";
print $str;
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I made table of unicode documents for perl. Please have a look at them, they are not so long documents.

perlunitut		6 pages	Very very short overview for unicode in perl + FAQ.
The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets (No Excuses!)		8 pages	About Charcter Set, Code Page, Unicode itself. Short History of Unicode.
perluniintro		12 pages	This is the first thing to read (I think).
Character Encodings in Perl		7 pages	all-in-one doc for encoding. Written by German Author.
perlunicode		20 pages	Main document of perl's unicode. Through and precise, or too much for beginner.
Perl Programming/Unicode UTF-8		15 pages	This document explains internal encoding of Perl (N8CS, utf-8) and also describe other problems. When you stumbled with 0x80-0xFF problem, this document explains the reason.