Perl regex reference
Found a Perl regex reference when trying to figure out how to capitalize the first letter of every word.
The way to do the capitalization involves using the right-hand term as a perl expression:
$string =~ s/\b(\w)/uc($1)/eg
So, the Perl uc() function is invoked on the pattern match buffer from the left-hand side. Clearly, the “e” modifier is useful for many other things.