title: Best way to substitute variables in plain text using PHP
body: <p>What's the best way to take some plain text (not PHP code) which contains PHP-style variables, and then substitute in the value of the variable. This is kinda hard to describe, so here's an example.</p>
  
  <pre><code>// -- myFile.txt --
  Mary had a little $pet.
  
  // -- parser.php --
  $pet = "lamb";
  // open myFile.txt and transform it such that...
  $newContents = "Mary had a little lamb.";
  </code></pre>
  
  <p>I've been considering using a regex or perhaps <code>eval()</code>, though I'm not sure which would be easiest. This script is only going to be running locally, so any worries regarding security issues and <code>eval()</code> do not apply <em>(i think?)</em>.</p>
  
  <p>I'll also just add that I can get all the necessary variables into an array by using <code>get_defined_vars()</code>:</p>
  
  <pre><code>$allVars = get_defined_vars();
  echo $pet;             // "lamb"
  echo $allVars['pet'];  // "lamb"
  </code></pre>