$r = qr/this-stuff/x;
$r = qr/this-stuff $more/x if $more;

[download]
where $more is either "| more-stuff", or "(*FAIL)". It doesn't matter whether $more is a plain string, or a $qr construct.

Now, I often assemble regexes from subparts. And I strongly prefer the subparts to be strings over compiled regexes. The compiled regexes contain extra sets of parens and setting of modifiers. I've made regexes long enough where the additional overhead of having all your subparts be qr// constructs made the difference between slow and "just takes too long".

You need a few backslashes less when using qr// instead of qq//. And there are some edge cases where the heuristic parsing of quoted constructs decides differently but they're obscure enough I can't even remember them.

In reply to Re: Composing regex's dynamically by JavaFan
in thread Composing regex's dynamically by John M. Dlugosz

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