in reply to Teaching Regular Expression Pattern Matching
...colleagues who tend to do a lot of elaborate string manipulation using only built-in string
functions—a common anti-pattern I've observed
Curiously, I more frequently see the converse anti-pattern, namely over-using regexes.
For example, I've often seen Perl beginners essaying:
when they should have been using:
if ($nodename =~ /$mynode/)
Apart from the obvious problem of embedded names (e.g. "freddy" v "fred"),
I've lost count of the number of times I've asked a Perl rookie to
consider what happens if $mynode contains regex metacharacters. Update: So I suggest you mention \Q and \E and quotemeta in your course.
if ($nodename eq $mynode)
I faced a similar Perl training problem a few years back and sent out an email with
seven specific word puzzle problems against the Unix "words" file (e.g. /usr/dict/words).
I offered some sort of prize for the winner IIRC.
All could be solved as one liners using: perl -ne 'your-program-here' words
or via a longer program, if you prefer.
For example: find all palindromes; find the longest word in the dictionary;
find all words that contain a particular letter four or more times;
find all words that start with "e", have "n" as their second last letter,
and are greater than seven characters in length;
find all words that are of even length and contain an even number of each and
every distinct vowel in the word. There are an endless number of interesting
word puzzles available.
You can further ask them to produce both regex and non-regex solutions,
to compare and contrast which approach is more appropriate for each problem.
It is not hard to invent problems where the regex solution is
vastly superior to the non-regex one, which may help convince them of
the power of regex.
Update: See also: