WareLogging, PerlCode, RegularExpressions.

* http://www.pcre.org/
* perldoc: [http://perldoc.perl.org/perlreref.html perlreref] - RegEx reference
* MasteringRegularExpressions

Little RegEx tricks:

 # Stuff in parentheses is slurped into the elements of @results
 @results = $string =~ m/stuff, (more stuff), and (some other stuff)/;

 # Here, $result is forced into list context and so contains (more stuff).
 # Without parentheses, it would just contain 1 or 0, depending on the pattern match.
 ($result) = $string =~ m/stuff, (more stuff), and some other stuff/;

Store a regex:

 $re = qr/whatever/;

= a thing which has recently bitten me =

When using s///x, keep in mind that whitespace continues to be significant in your substitution, which is after all a string.

For example, this will be fine:

 $block =~ s/([^"\n]) # not a double-quote or newline
             \n       # end-of-line
             ([^\n])  # not a newline
            /$1$newlines{$key}$2/xgs;

While this will be all kinds of problematic:


 $block =~ s/([^"\n]) # not a double-quote or newline
             \n       # end-of-line
             ([^\n])  # not a newline
            /$1
             $newlines{$key}
             $2
            /xgs;

Incidentally, I think this is better written as:

 $block =~ s/(?<=[^"\n]) # not a double-quote or newline
             \n          # end-of-line
             (?=[^\n])   # not a newline

            /$newlines{$key}/xgs;