<p><pre><code> for a in `ls -1 /usr/bin/`; do whatis "$a"; done | less
</code></pre>
That prints out a list of every command in /usr/bin with a one-line description.<p>sed (transforming pipe with regular expressions) and file (try to identify a file type based on headers and other metadata) are also quite handy.<p>If you find the post interesting, check out Kernighan & Pike's _The Practice of Programming_.