cat with output of sed
<p>I'd like to delete all lines starting with <code>##</code> in a file (<code>file.a</code>) and replace them with all the lines of another file (<code>file.b</code>). The lines to be deleted from <code>file.a</code> appear first in that file (there are no lines preceding them).</p>

<p>The long way would be:</p>

<pre><code>sed -i '/##/d' file.a
cat file.b file.a &gt; file.c
mv file.c file.a
</code></pre>

<p>Is there a short (in line) way?</p>