title: Check if pattern exists in a keys of hash
body: <p>I have a hash of following pattern</p>
  
  <pre><code>my %hash_table(
       23                =&gt; someintegertype,
       type              =&gt; somestringtype,
       12_someidentifier =&gt; someveryproblematictype
  );
  </code></pre>
  
  <p>How do I check if pattern that <code>12_someidentifier</code> key follows exists in the hash or not? If so, I need to know the value in the form of <code>true</code> or <code>false</code>.</p>
  
  <p>::UPDATE::
  I wanted to check if the regex or pattern such as  <code>{[\d]_[\w+]}</code> exists or not?</p>