How to replace slash into underscore in a file name?
<p>I want to save a file with mail_number name. I am using 

<blockquote>
  <p><code>$file_name =  $request['mail_number'] . '.' . $extension;</code></p>
</blockquote>

<p><br>And it is works. But the problem is, when my mail_number name is include slash('/') character, it won't saved. Do you know how to replace slash('/') with underscore('_') when the file is saved?</p>