title: when "bash -c" will cause child shell created?
body: <p>on my centos7.4 server,if run</p>
  
  <pre><code>bash -c "python -m SimpleHTTPServer"
  
  pstree -sp 10784 (PID of python server)
  </code></pre>
  
  <p>will show</p>
  
  <pre><code>systemd(1)───sshd(922)───sshd(11595)───sshd(11597)───bash(11598)───python(11617)
  </code></pre>
  
  <p>and with</p>
  
  <pre><code>bash -c "python -V &amp;&amp; python -m SimpleHTTPServer"
  </code></pre>
  
  <p>I got</p>
  
  <pre><code>systemd(1)───sshd(922)───sshd(11595)───sshd(11597)───bash(11598)───bash(11638)───python(11640)
  </code></pre>
  
  <p>so why a child shell created in the 2nd command?</p>