title: What condition is this checking for: if [ -z $1 ]
body: <p>I have three if conditions in a shell script I have been given, can I be assisted with what they each mean in English. Also, how would I use the man pages to find out similar commands in the future?</p>
  
  <p>The conditions are as follows:</p>
  
  <ol>
  <li><p><code>if [ -z $1 ]</code></p></li>
  <li><p><code>if [ ! -r $1 ]</code> </p></li>
  <li><p><code>if [ -n $3 ]</code></p></li>
  </ol>