<p>Hi looking for some help in explaining what this line is doing. I am completely lost in what it is saying. I know it is exiting there because I can see my log line 25 but NOT log line 27.</p>
<pre class="lang-bash prettyprint-override"><code>[[ `hostname` =~ -([0-9]+)$ ]] || exit 1
</code></pre>
<pre class="lang-yaml prettyprint-override"><code>      initContainers:
      - name: init-mysql
        image: mysql:5.7
        command:
        - bash
        - &quot;-c&quot;
        - |
          set -ex
          # Generate mysql server-id from pod ordinal index.
          echo &quot;Running line25&quot; &gt;&gt; /var/lib/mysql/temp.log
          [[ `hostname` =~ -([0-9]+)$ ]] || exit 1
          echo &quot;Running line27&quot; &gt;&gt; /var/lib/mysql/temp.log
</code></pre>

user3008410
<p>It runs the <code>hostname</code> command, and then compares its output to the regular expression <code>-([0-9]+)$</code>. The parentheses are redundant, so it could be simplified to <code>-[0-9]+$</code>; this is &quot;a string that ends with <code>-</code> and 1 or more digits&quot;.</p>
<p>If the output of <code>hostname</code> doesn't match the expression, <code>exit 1</code> is called. You can look at the output of <code>hostname</code> separately to see its value.</p>
