code: def isset(alias_name):
      
      warnings.warn('Will be removed in v1.0', DeprecationWarning, stacklevel=2)
      raw_value = read(alias_name, allow_none=True)
      if raw_value:
          if re.compile(r'.+://.+:\d+').match(raw_value):
              return True
          else:
              warnings.warn('"{0}_PORT={1}" does not look like a docker link.'.format(alias_name, raw_value), stacklevel=2)
              return False
  
      return False
docs: Return a boolean if the docker link is set or not and is a valid looking docker link value.
  
      Args:
          alias_name: The link alias name