code: def exec_helper(self, cmd, builddir):
          ''' Execute the given command, returning an error message if an error occured
              or None if the command was succesful.'''
          try:
              child = subprocess.Popen(cmd, cwd=builddir)
              child.wait()
          except OSError as e:
              if e.errno == errno.ENOENT:
                  if cmd[0] == 'cmake':
                      return 'CMake is not installed, please follow the installation instructions at http://docs.yottabuild.org/#installing'
                  else:
                      return '%s is not installed' % (cmd[0])
              else:
                  return 'command %s failed' % (cmd)
          if child.returncode:
              return 'command %s failed' % (cmdf exec_helper(self, cmd, builddir):
          ''' Execute the given command, returning an error message if an error occured
              or None if the command was succesful.'''
          try:
              child = subprocess.Popen(cmd, cwd=builddir)
              child.wait()
          except OSError as e:
              if e.errno == errno.ENOENT:
                  if cmd[0] == 'cmake':
                      return 'CMake is not installed, please follow the installation instructions at http://docs.yottabuild.org/#installing'
                  else:
                      return '%s is not installed' % (cmd[0])
              else:
                  return 'command %s failed' % (cmd)
          if child.returncode:
              return 'command %s failed' % (cmd)
docs: Execute the given command, returning an error message if an error occured
              or None if the command was succesful.