$URL =~ s/&/&/g;

# numeric entities
$URL =~ s/&#(\d+);/pack('c', $1)/ge;

# hex escapes
$URL =~ s/%(\d{2})/pack('c', $1)/ge;

# 'decimal' IP
$URL =~ s/(\d{5,})/join('.', unpack('C4', pack('N', $1)))/ge;