#!/usr/bin/env perl

use strict;
use warnings;

{
    my %char_for_ent = qw{&quot; " &apos; ' &lt; < &gt; >};
    my $re = qr/(?x: ( @{[ join '|', keys %char_for_ent ]} ) )/;
    sub ent2char { $_[0] =~ s/$re/$char_for_ent{$1}/g; $_[0] }
}

print "IN:  ${_}OUT: ", ent2char($_) while <DATA>;

__DATA__
I said, &quot;My name&apos;s Ken&quot;.
<pre>Here&apos;s some &lt;em&gt;emphasis&lt;/em&gt;.</pre>