title: Query prolog with PHP
body: <p>I am trying to make a sudoku game with PHP and prolog, the idea is to use prolog program to solve the sudoku then get the results via PHP, I have write this code down but I'm getting a empty output
  I have even try to use <code>var_dump</code> to test and i'm getting <code>string '' (length=0)</code> 
  here is my code:</p>
  
  <pre><code>&lt;!DOCTYPE&gt;
  &lt;html xmlns="http://www.w3.org/1999/xhtml"&gt;
  &lt;head&gt;
  &lt;meta http-equiv="Content-Type" content="text/html; charset=utf-8" /&gt;
  &lt;title&gt;Soduku&lt;/title&gt;
  &lt;link href="style.css" rel="stylesheet" type="text/css"&gt;
  &lt;/head&gt;
  
  &lt;body&gt;
  &lt;div id="content"&gt;
  &lt;?php
  
  $output=exec("\"c:/Program Files (x86)/swipl/bin/swipl-win.exe\" -g \"test,halt\" -t \"halt(1)\" test.pl ");
  var_dump($output);
  echo $output;
  echo"&lt;pre&gt;";
  print_r($output);
  echo"&lt;/pre&gt;";
  
  ?&gt;
  
  
  &lt;/div&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>my code after edition</p>
  
  <pre><code>&lt;!DOCTYPE&gt;
  &lt;html xmlns="http://www.w3.org/1999/xhtml"&gt;
  &lt;head&gt;
  &lt;meta http-equiv="Content-Type" content="text/html; charset=utf-8" /&gt;
  &lt;title&gt;Soduku&lt;/title&gt;
  &lt;link href="style.css" rel="stylesheet" type="text/css"&gt;
  &lt;/head&gt;
  
  &lt;body&gt;
  &lt;div id="content"&gt;
  &lt;?php
  
  exec('"c:\\Program Files (x86)\\swipl\\bin\\swipl-win.exe" -g "st,halt" -t "halt(1)"  -s test.pl',$output,$return_var);
  var_dump($output);
  echo $return_var;
  
  
  ?&gt;
  
  
  &lt;/div&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>it display this result</p>
  
  <pre><code>array (size=0)
    empty
  0
  </code></pre>