What is your latest useful Perl one-liner (or a pipe involving Perl)?

Please see my slides for "A Field Guide To The Perl Command Line Options."

Squid log files. They're great, aren't they? Except by default they have seconds-from-the-epoch as the time field. Here's a one-liner that reads from a squid log file and converts the time into a human readable date:

perl -pe's/([\d.]+)/localtime $1/e;' access.log

With a small tweak, you can make it only display lines with a keyword you're interested in. The following watches for stackoverflow.com accesses and prints only those lines, with a human readable date. To make it more useful, I'm giving it the output of tail -f, so I can see accesses in real time:

tail -f access.log | perl -ne's/([\d.]+)/localtime $1/e,print if /stackoverflow\.com/'