Backslashes are a pain in the back. Slash. The problem is that your regex ends up being /TRicky\(.*?)\endTricky/ because your variables interpolate. When that gets compiled as a regex, it's a problem because the trailing backslash of "TRicky\" has escaped the opening parenthesis. I would suggest using my $StartTag = qr/TRicky\\/; my $EndTag = qr/\\endTricky/; The qr// operator will keep things properly backslashed later, because the content is treated like a regex.