title: bash "-e" puzzler: script file ended unexpectedly
body: <p>To make things clear, I would short my bash script:   </p>
  
  <pre><code>#!/bin/bash -e  
  
  p_time=$(expr 0 - 0)
  echo ?
  echo "process time(sec) is: " ${p_time}  
  </code></pre>
  
  <p>The file would end before "echo ?", but if I change "p_time=$(expr 0 - 0)" to "p_time=$(expr 3 - 0)", the file would end correctly.<br>
  However, if I removed "-e" in the first sentence, the file ended correctly too.<br>
  Why would this happen?</p>