Recently I was asked what unix utility was missing the most functionality; I answered locate, as it'd be nice if it knew about file contents. 
<p>
I had been thinking about how to nicely search files and had tried <a href="http://www.rpcurnow.force9.co.uk/mairix/">mairix</a> for my maildir'd email, and <a href="http://webglimpse.net/">glimpse</a>. mairix was functional, but glimpse's nightly cache rebuilds were getting ridiculously lengthly (4+ hours).
</p>

<p>At the last HPM, NathanPowell pointed me in the direction of <a href="http://www.beagle-project.org">Beagle</a>, which helpfully enough comes with a seperable command-line and graphical interface. Guess which one I installed? ;)
</p>

<p>Beagle uses linux's kernel Inotify feature to receive new files to index, so there's no need to rebuild a cache, but rather only add newly added or updated files. There's a 'beagled' daemon that you just leave running that automatically takes care of this updates. 
</p>

<p>The first caveat is that the documentation says beagle indexes <a href="http://beagle-project.org/Indexing_Data">everything</a>, which isn't true. It won't index dotfiles or dotdirectories. So, if you happen to have a ~/.maildir, you need to rename it before it will be indexed. </p>

<p>The second caveat is that beagled will probably continue to use a bunch of memory; we'll see how this impacts life on my laptop.
<pre>
phaller  25402  0.1 10.9  88568 41412 ?        Sl   00:57   0:29 beagled --debug /usr/lib/beagle/BeagleDaemon.exe --bg
phaller  30316  1.1  7.7  56004 29152 ?        Sl   04:33   0:23 beagled-helper --debug /usr/lib/beagle/IndexHelper.exe
</pre>
</p>

Finally, beagle outputs references in URI format, so I wrote a quick perl script to handle my command-line tossing of output to other programs:
<div class='source'>
#!/usr/bin/perl

my $q = join(' ', @ARGV);

open(my $fh, "beagle-query $q |");
for(<$fh>) {
        s#^file://## and do {
                print $_;
                next;
        };

        print STDERR $_;
}

close($fh);
</div>
<hr /><tt>That's hot.  I didn't realize there was a command line interface.  Hmm, I suspect this will make it highly usable. - nathan</tt>