$uncompiled_re = '(?i-xsm:turtle|fish)';
mysub($uncomiled_re);

$compiled_re = qr/turtle|fish/i;
mysub($comiled_re);

##</code><code>##

$uncompiled_re = "(?i-xsm:\\w)";
mysub($uncomiled_re);

$compiled_re = qr/\w/i;
mysub($comiled_re);