That code (unpack 'W' specifically) only works in 5.10. Below is a version that works in 5.8+ (when unicode support was added), and a reverse function for 5.8+ that safe for use on untrusted strings.

sub escape_5_10 {
   join '',
   map { $_ > 255               ? sprintf('\\x{%04X}', $_)
       : chr() =~ /[[:cntrl:]]/ ? sprintf('\\x%02X', $_)
       : quotemeta(chr())         
       }
   unpack('W*', @_ ? $_[0] : $_)
}


sub escape {
   join '',
   map { ord() > 255   ? sprintf('\\x{%04X}', ord())
       : /[[:cntrl:]]/ ? sprintf('\\x%02X', ord())
       : quotemeta()         
       }
   map /./gs,
   @_ ? $_[0] : $_
}

sub unescape {
   my $s = @_ ? $_[0] : $_;
   $s =~ s/
      \G
      (?: \\x \{ ([0-9a-fA-F]+) \}
      |   \\x ([0-9a-fA-F]{1,2})
      |   \\(.)
      |   # No escapes
      )
      ([^\\]*)
   /
      ( defined($1) ? chr(hex($1))
      : defined($2) ? chr(hex($2))
      : defined($3) ? $3
      : ''
      ) . $4
   /xesg;
   $s
}


# XXX Assumes. Good enough. Avoids warn.
binmode STDOUT, ':encoding(UTF-8)';

my $s = '<3'          # \W and \w
      . chr(0x04D2)   # wide char
      . "\cC";        # ctrl char
print("$s\n");

$s = escape($s);
print("$s\n");

$s = unescape($s);
print("$s\n");
[download]

Update: Functions now default to using $_ is no arg was supplied.