title: How to check if command is exists?
body: <p>I need to detect if app is present in system. 
  I use for it std.process the next code is trow exception if executable command do not exists:</p>
  
  <pre><code>try
  {
      auto ls = execute(["fooapp"]);
      if (ls.status == 0) writeln("fooapp is Exists!\n");
  }
  
  catch (Exception e)
  {
          writeln("exception");
  }
  </code></pre>
  
  <p>Is there any better way to check if app is exists without throwing exception? </p>