use Benchmark('countit');

$code = '$str =~ s/(?<=[a-z])(?=[A-Z])/_/g';
$t = countit(5, '$str="BuyACaseOfCamels";' . $code);
$count = $t->iters ;
print "$count loops of $code\n";

$code = '$str =~ s/([a-z]+)(?=(.?))/ $1 . (length($2) ? "_" : "") /ge';
$t = countit(5, '$str="BuyACaseOfCamels";' . $code);
$count = $t->iters ;
print "$count loops of $code\n";

$code = '$str =~ s/([a-z]+)/$1_/g; $str =~ s/_$//';
$t = countit(5, '$str="BuyACaseOfCamels";' . $code);
$count = $t->iters ;
print "$count loops of $code\n";

##</code><code>##

  perl ccase.pl
1686588 loops of $str =~ s/(?<=[a-z])(?=[A-Z])/_/g
1194666 loops of $str =~ s/([a-z]+)(?=(.?))/ $1 . (length($2) ? "_" : "") /ge
1520477 loops of $str =~ s/([a-z]+)/$1_/g; $str =~ s/_$//

  perl ccase.pl
1793776 loops of $str =~ s/(?<=[a-z])(?=[A-Z])/_/g
1286561 loops of $str =~ s/([a-z]+)(?=(.?))/ $1 . (length($2) ? "_" : "") /ge
1466174 loops of $str =~ s/([a-z]+)/$1_/g; $str =~ s/_$//

  perl ccase.pl
1760558 loops of $str =~ s/(?<=[a-z])(?=[A-Z])/_/g
1336044 loops of $str =~ s/([a-z]+)(?=(.?))/ $1 . (length($2) ? "_" : "") /ge
1492832 loops of $str =~ s/([a-z]+)/$1_/g; $str =~ s/_$//