Re^2: Regex help

[graff]

Is that documented behaviour? Where?

Yes, in perlre, as follows:

An unescaped "$" or "@" interpolates the corresponding variable, while escaping will cause the literal string "\$" to be matched.

(Though in the version of the perlre man page I have installed, for perl 5.8.8, this sentence comes second in a paragraph that begins with:

You cannot include a literal "$" or "@" within a "\Q" sequence."

I can understand that some might consider this obscure.)

[pKai]

Those remarks in perlre are not specific to character classes, and one regularly thinks these character classes are more special.

Explicit mentioning of $ being special in character classes is found in perlretut#Using-character-classes:

…The special characters for a character class are -]\^$ (and the pattern delimiter, whatever it is). ] is special because it denotes the end of a character class. $ is special because it denotes a scalar variable.…

So indead not only punctation variables are being expanded:

E:\Temp>perl -Mstrict -we "my $foo=7;die qq(matched '$&'\n) if '123456
+7rab_.'=~/[${foo}bar]+/"
matched '7rab'