From TFA:<p><pre><code> grep '[[:punct:]]$' files
</code></pre>
I suspect the author has grep aliased to `egrep` or `grep -E` because [:punct:] is an extended regular expression and GNU grep defaults to basic RE mode.
Before you invest time in grep, take a look at ack-grep <a href="http://betterthangrep.com/" rel="nofollow">http://betterthangrep.com/</a>.<p><pre><code> ack-grep --thppt</code></pre>