What is the difference between these os.popen calls?
<p>I have two scripts:</p>

<p>The first works well:</p>

<pre><code>import os
os.popen(‘grep abc filename’)
</code></pre>

<p>The second does not work:</p>

<pre><code>import os
os.popen(‘grep abc’ + ’filename’)
</code></pre>

<p>But this does:</p>

<pre><code>os.popen(‘grep abc filename’ + ‘&gt;’ + ‘filename2’)
</code></pre>

<p>So, I can’t understand the difference. What is wrong about the second version?</p>