in reply to matching constants within a regular expression?

Thank you for searching before you ask! That is always appreciated. One little note about your link though: Perlmonks has a special linking system that you should use. Your link goes to, while many monks, myself included, use, which means we aren't logged in when we follow your link.

Instead, you should link like this: [id://293323] or [use of constants in regex substitutions?], which will yield use of constants in regex substitutions?. (See What shortcuts can I use for linking to other information?)

Now on to your question. :-) The node you linked to does in fact include the answer, which I will explain for you. You want to use: print "attribute 0=\t$1\n" if m/${\ATTRIBUTE_0}='(.*)'/;

Here's the reasoning. When you create a constant, like ATTRIBUTE_0 and ATTRIBUTE_1, you're really creating a special subroutine. The reason it works is because perl knows you aren't going to pass it any parameters, so it can insert the value from the sub at compile time.

This means that when you use the constant in your regex, you need to access it like a subroutine. You do this by creating a reference to its value and dereferencing that reference. The \ creates the code reference and the ${} dereferences it. For more info see: perlref.

I hope this helps!