use Benchmark;

@array = ('elementary school', 'blah blah blah', 'stuff', 'hello', 'ya
+y');

timethese(100000, {
    'one line' => '&one_line',
    'multi line' => '&multi_line'});

sub one_line
 {
   do {s/\s+/\t/; s/elementary/my dear Watson/g;} for @array;
 }

sub multi_line
 {
   for ( @array ) {
       s/\s+/\t/;
       s/elementary/my dear Watson/g;
   }
 }
[download]

This can't be true, because:

d:\>perl -MO=Deparse -e "do {s/\s+/\t/; s/elementary/my dear Watson/g;
+} for @array;"
foreach $_ (@array) {
    s/\s+/\t/;
    s/elementary/my dear Watson/g;;
}
-e syntax OK
[download]

You machine probably was overloaded with some extra tasks second time. And I beleive multiline version compiled into the same code internally.

Sweet! writing obfusicated code just got a lot harder.
Maverick goes pouring through the docs on B

/\/\averick

holy crap! that is the coolest thing i have seen in forever, I had NO idea you could do that! -MO=Deparse... wow, I am angered that i can only ++ this once, that is one of the most useful things I have seen in forever! Thank you!

Thanks on two accounts (the second being: reading your message, now I have an idea how to use Benchmark).

The results here confirm what you observed:

Benchmark: timing 500000 iterations of multi line, one line...
multi line: 12 wallclock secs (12.31 usr +  0.00 sys = 12.31 CPU)
  one line: 16 wallclock secs (14.64 usr +  0.00 sys = 14.64 CPU)
[download]