title: PHP dollar sign in strings
body: <p>I don't unserstand why PHP doesn't make replacements in strings containing dollar signs.
  Look at the following example:</p>
  
  <pre><code>&lt;?php
  error_reporting (E_ERROR | E_WARNING | E_PARSE | E_NOTICE);
  $var = 1024;
  $str = '$var';
  echo $str, '&lt;br&gt;', "$str";
  </code></pre>
  
  <p>Output is <em>$var $var</em>. Why is it so? Everything is clear with first <code>echo</code> parameter, but I expected that the last parameter will give a different result (1024), because it contains dollar sign encapsulated by double quotes, so it should be interpreted as variable and replaced to 1024. Where am I going wrong?</p>