title: exec.Command with variable arguments
body: <p>I'm trying to pass an argument to an exec.Command. <em>Part</em> of that argument is a variable.</p>
  
  <pre><code>a := fileName
  exec.Command("command", "/path/to/"a).Output()
  </code></pre>
  
  <p>I'm not sure of how to approach this, I'm thinking I need to fully form the argument before I even pass it, but I'm also struggling with that option. I'm not sure how to do something like:</p>
  
  <pre><code>a := fileName
  arg := "/path/to/"a
  exec.Command("command", arg).Output()
  </code></pre>