title: Filter square brackets on Kibana
body: <p>I'm struggling to filter square brackets on my log messages in Kibana.
  Suppose I have the messages:</p>
  
  <pre><code>[BOOK] The Book 32 was sold
  Exception on buying BOOK
  </code></pre>
  
  <p>And I want to filter only messages having exactly <code>[BOOK]</code> (so I should get only the first one).</p>
  
  <p>I have tried filtering free text with all kinds of escaping I could think of:</p>
  
  <pre><code>[BOOK]
  "[BOOK]"
  \[BOOK\]
  "\[BOOK\]"
  \\[BOOK\\]
  
  </code></pre>
  
  <p>And also tried filtering by the message field:</p>
  
  <pre><code>message: [BOOK]*
  message: "[BOOK]*"
  message: \[BOOK\]*
  message: "\[BOOK\]*"
  </code></pre>
  
  <p>But Kibana seems to simply ignore the square brackets and always brings both messages, highlighting only the <code>BOOK</code> word.</p>
  
  <p>How can I force it search for the <code>[]</code>?</p>