#!/usr/local/bin/perl

use Benchmark;

my $str = "the %0A quick %2b brown %63 fox  %63 jumped %24 over %7e the %4f%45 lazy %25 dog";
 
timethese (500000, {
   'myway' => sub {
        $_ = $str;
        while (/%[0-9A-Fa-f]{2}/) {
            $_ = $&;
            /[0-9A-Fa-f]{2}/;
            $ob[0] = hex($&);
            $temp = pack("C*", @ob);
            $name =~ s/%[0-9A-Fa-f]{2}/$temp/;
            $_ = $name;
            }
        },
   'regexpway' => sub {
        $_ = $str;
        s/%([a-fA-F0-9]{2})/pack("C", hex($1))/eg;
        },
            }); 

Benchmark: timing 500000 iterations of myway, regexpway...
     myway: 23 wallclock secs (21.99 usr +  0.00 sys = 21.99 CPU)
 regexpway: 57 wallclock secs (57.58 usr +  0.00 sys = 57.58 CPU)