Why a string surrounded with single quotes will not interpolate the variable names it contains in PHP, while with double quotes it does?
<blockquote>
  <p><strong>Possible Duplicate:</strong><br>
  <a href="http://facebook.stackoverflow.com/questions/3446216/difference-between-single-quote-and-double-quote-string-in-php">Difference between single quote and double quote string in php</a>  </p>
</blockquote>



<p>We can include the name of a variable right inside a text string and have the value inserted in its place if we surround the string with double quotes instead of single quotes. </p>

<p>why does not it works in case of single quotes?</p>
