#!/usr/local/bin/perl -w

use strict;

my $desc = "I %2Blike %3A cheese";
my ($str, @ob);

print "TEST: ",test(),"\n";<br>

sub test {
    $_ = $desc;
    while (/%[0-9A-Za-z]{2}/) {
        $_ = $&;
        /[0-9A-Za-z]{2}/;
        $ob[0] = hex($&);
        $str = pack("C*", @ob);
        $desc =~ s/%[0-9A-Za-z]{2}/$str/;
        $_ = $desc;
        }
    return $desc;
}

returns:

TEST: I +like : cheese