Firstly, you've done nothing wrong in replying twice to the same node. You've done this in a perfectly acceptable fashion: asking different questions which stem from the same previous response. Here's an example of me doing the exactly same thing in last 24 hours: Perl/TK borderwidth question - note the two Re^3: Perl/TK borderwidth question responses. Updating your node (and perhaps sending a /msg indicating such updating) is the more usual way; however, in this instance, you've done the right thing: thunderbolts from the gods may prove me wrong. *gulp* :-)

My personal preference for links to books is that they target the publisher not some arbitrary vendor. A vendor will not advertise books that they do not have in stock. Mastering Regular Expressions is published by O'Reilley and this company, in particular Tim O'Reilley, has been a particularly good friend to Perl over the years - the company your posted link refers to shows no such affiliation. The link I would have provided for this book is: Mastering Regular Expressions (i.e. actual markup: [http://shop.oreilly.com/product/9781565922570.do|Mastering Regular Expressions] [I do have a copy of that book myself and - yes - it's wonderful! :-)]

OK - Off the soap box and back to the code.

Wherever you have non-capturing parentheses containing alternation (e.g (?:x|y|z)), it's usually better to avoid backtracking with the (?>...) construct (e.g. (?>x|y|z)). See perlre - Backtracking, perlre - Extended Patterns and pp. 102-107 in Friedl's book (check the index - page numbers may differ in your version).

You say: "As a result, the regexps in this code are rather long, but I hope still readable.". There's absolutely no reason for them to be unreadable due to length: just use the x option. Furthermore, for those variables not dependent on a loop variable, you can compile them outside of the loop once. Here's an example:

sub some_function {
    my $re = qr{
        \A               # start of string
        (?> x | y | z )  # match exactly one of x, y or z
        \z               # end of string (ignore optional terminal new
+line)
    }x;

    while (<>) {
        if (/$re/} {
            # do something based on successful match
        }
    }
}
[download]

Finally, I am absolutely not going to tell you to adopt any particular coding style; however, I am going to urge you to adopt a coding style that's easy for you and others to read. Have a look around the Monastery, see how other Monks write their code, then pick something you're comfortable with. Beyong the indentation issues, the code you presented at the start of this thread was superior to what you now have. If you seriously don't understand what you read in perlstyle, then please ask for clarification.