title: Mac command line say "bad math expression: operand expected at end of string"
body: <p>On macbook terminal, when i hit the command TAB key after <code>ls</code>.
  Terminal say error.</p>
  
  <pre><code>$ ls
  _complete:96: bad math expression: operand expected at end of string
  </code></pre>
  
  <p>This example is <code>ls</code>, but other all command has same trouble.
  I rebooted mac but trouble has not cleared.</p>
  
  <p>What's happen do you know?</p>
  
  <hr>
  
  <p>Mac was shutdown by himself automatically, and repaired before i knew it.</p>
  
  <p>OS is:  OS X El Capitan.</p>