Re^3: Regex error when [] occurs in file..

[Joost]

Are all 'special variables' ($&, $N (N is integer)) expanded in that way too?

All variables are expanded that way, special or not:

my $var = '[ab]';
my $string = '12a3434';
print "match" if $string =~ /$var/;

See also quotemeta and the \Q and \E escape sequences.