I don't have a good idea of your difficulties, but here's a generalized approach. I can't provide a working example at the moment, so the following is untested handwaving.

The  (*SKIP)(*FAIL) variable-width negative look-back hack works by messing up a match of something you need to have for an overall match. For a large regex, I tend to take the approach of factoring regex elements: 

# stuff we want to capture
my $capture_this = qr{ ... }xms;
my $capture_too  = qr{ ... }xms;
my $capture_also = qr{ ... }xms;
my $capture_more = qr{ ... }xms;

# stuff we want to cause match failure if before certain other stuff
my $avoid_this = qr{ ... }xms;
my $avoid_too  = qr{ ... }xms;
my $avoid_also = qr{ ... }xms;
my $negatory   = qr{ (?> [aeiou]+ | f[eio]e? | $avoid_too) }xms;

# stuff we need for an overall match, may or may not be captured
my $needed_for_match = qr{ ... }xms;
my $needed_too       = qr{ ... }xms;

my $string = get_stringy_stuff();

my ($this, $too, $also, $yet_another) = $string =~ m{
    \A
    ($capture_this)
    ($capture_too)
    ...
    (?> (?> $avoid_this | $avoid_too | $avoid_also | etc) $needed_for_
+match (*SKIP)(*F))?
    $needed_for_match  # needed for overall match
    ($capture_also)
    ...
    (?> $negatory $needed_too (*SKIP)(*FAIL))?
    ($needed_too)  # needed for overall match, also captured
    \z                                 
    }xms;

do_something_with($this, $too, $also, $yet_another);

[download]

Give a man a fish:  <%-(-(-(-<

In reply to Re^3: Another Look behind by AnomalousMonk
in thread Another Look behind by dominic01

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.