Like many Unix commands, if you don&#x27;t give cat any files to read, it reads from stdin instead. So first he runs the command (as he typed it), and then while cat is waiting for input he pastes in whatever he copied from the website.<p>Another handy convention is the magic &quot;-&quot; filename (which is not actually a file). Many tools interpret that to mean stdin&#x2F;stdout. For example here is a trick to copy a tree of files:<p><pre><code>    tar cf - src | (cd dest &amp;&amp; tar xvf -)</code></pre>