whole_func_string: function safeExec(cmd, cb) {
      try {
        utils._exec(cmd, cb);
      } catch (e) {
        cb(e, null);
      }
    }
func_code_string: function safeExec(cmd, cb) {
      try {
        utils._exec(cmd, cb);
      } catch (e) {
        cb(e, null);
      }
    }
func_documentation_string: Node's built in `exec` function sometimes throws outright,
  and sometimes has a callback with an error,
  depending on the type of error.
  
  This unifies that interface.