use Benchmark; timethese(500, { 'or pattern' => \&orpattern, 'many patterns' => \&manypatterns }); sub init { %sub_hash = (John => Mike, Jack => Mark, Joe => Moe); $string = "Dear John!.\nI've run off with Jack and Joe.\nSue\n\n" x 1000; } sub orpattern { init; my $keys = join '|', map "\Q$_\E", keys %sub_hash; my $keys_REx = qr/$keys/; $string =~ s/($keys_REx)/$sub_hash{$1}/g; return $string; } sub manypatterns { init; my %patterns = map { qr/$_/ => $sub_hash{$_} } keys %sub_hash; foreach $pat (keys %patterns) { my $replace = $patterns{$pat}; $string =~ s/$pat/$replace/g; } return $string; } #### %substitute_hash = ( Jack => Chris, Chris => Jaquline );