title: Shell session exited by itself after issuing command "exec<>5"
body: <p>When issued two commands below in Linux or MacOS, the Shell session exited and no any error message displayed.</p>
  
  <pre><code>➜  ~  sh
  sh-3.2$ exec&lt;&gt;5
  sh-3.2$ exit    ==&gt; 'exit' was issued by the shell itself!
  </code></pre>
  
  <p>Is this a defect of '/bin/sh'? Can anyone provide any insight?</p>
  
  <p>/bin/sh on my RHEL:</p>
  
  <blockquote>
    <p>-sh-4.1$ sh --version
    GNU bash, version 4.1.2(1)-release (x86_64-redhat-linux-gnu)
    Copyright (C) 2009 Free Software Foundation, Inc.</p>
  </blockquote>
  
  <p>/bin/sh on my MacOS:</p>
  
  <blockquote>
    <p>➜  ~  sh --version
    GNU bash, version 3.2.57(1)-release (x86_64-apple-darwin14)
    Copyright (C) 2007 Free Software Foundation, Inc.</p>
  </blockquote>