use Benchmark;

$iterations = 1000000;     

$name1 = "Alternation"; 
$code1 = ' $_="ABBA"; s/(A|B)/X/g; ';

$name2 = "Class"; 
$code2 = ' $_="ABBA"; s/[AB]/X/g; ';

$name3 = "Substitution"; 
$code3 = ' $_="ABBA"; s/A/X/g; ';

$name4 = "Transliterate"; 
$code4 = ' $_="ABBA"; tr/A/X/; ';

timethese($iterations, {$name1 => $code1, 
						$name2 => $code2,
						$name3 => $code3,
						$name4 => $code4,
						} );

__END__

C:\>perl test.pl

Benchmark: timing 1000000 iterations of Alternation, Class, Substitution, Transliterate...

Alternation:   36 wallclock secs (35.92 usr +  0.00 sys = 35.92 CPU) @ 27839.64/s  (n=1000000)
     Class:    23 wallclock secs (23.12 usr +  0.00 sys = 23.12 CPU) @ 43252.60/s  (n=1000000)
Substitution:  20 wallclock secs (20.81 usr +  0.00 sys = 20.81 CPU) @ 48053.82/s  (n=1000000)
Transliterate:  8 wallclock secs ( 8.07 usr +  0.00 sys =  8.07 CPU) @ 123915.74/s (n=1000000)

C:\>