title: -z option inside if condition in shell script
body: <p>Can someone post me the significance of -z option while writing if condition using shell scripts.</p>
  
  <p>Let me paste the exact condition what I am looking at</p>
  
  <pre><code>if [[ "x$do_clean_flag" = "x-clean" &amp;&amp; -z "$show_me_flag" &amp;&amp; "$verify" = true ]]
  </code></pre>