title: Bash Script - Exclamation Point within Variable Reference
body: <p>I'm looking over a script (which has been used successfully in the past) which contains the following:</p>
  
  <pre><code>node=1
  while :
  do
      userKey=WEB_${node}_USER
      userVal=`echo ${!userKey}`
  </code></pre>
  
  <p>I have not been able to figure out why an exclamation point would be added to a variable reference like this. What purpose does "!" serve in this context?</p>
  
  <p>It's rare for me to do much scripting so if I am missing any details please let me know and I will try to provide more information. I have not been able to find this answer elsewhere.</p>
  
  <p>Thanks in advance!</p>