title: If an regex expression is in a string , how can I exec the regex?
body: <p>Like this : </p>
  
  <pre><code>$pattern = " /(\d{4})\s*-\s*(\d{2})\s*-\s*(\d{2})\s*(\d{2}):(\d{2}):(\d{2})\.(\d+)/" ;
   $_ = "1972-01-01 00:00:00.0" ;
  </code></pre>
  
  <p>How can I execute the regex in the $Pattern by <strong>using Perl</strong> ? </p>