Reading the replies above, I get the impression that looking at the theoretical Regular Expression material, while probably good to learn, is limited in its applicability to Perl regular expressions.

It would appear that the path to enlightenment is through practice, and not pedagoguery.

This has been my experience. "Regular expressions," as they have evolved (into ir-regular expressions, as others have noted), are the most counterintuitive things I have encountered in programming.

Here's my favorite example of this conceptual orneriness. What will the regex  /(b*)/ capture when run against the string  'aaaaabbbb' and where (i.e., at what character position offset)? Knowing as we do that  * matches "as much as possible" of something, I'd almost be willing to bet money that even the most regex-savvy will experience at least a minor knee-jerk twitch in the general direction of "it matches  'bbbb' at offset 5." But surprise, surprise:

c:\@Work\Perl\monks>perl -wMstrict -le
"my $s = 'aaaaabbbb';
 print qq{matches '$1' at offset $-[1]} if $s =~ /(b*)/;
"
matches '' at offset 0
[download]

The answer to the puzzle is that "as much as possible" cheats and leaves out the leftmost and equally important part of the "leftmost longest" incantation that should properly be used^* to describe all regex matching. Bottom line: No amount of theoretic or pedagogic vaccination can build up your natural antibody resistance to this sort of thought-bug better than daily exposure to a wide variety of regex challenges. Good luck in your experimentation, and may you make many mistakes, for I know no better way to learn this stuff.

* Old Whateley and his son Wilbur knew the dangers of incomplete and possibly maliciously altered incantations.