<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _shallow_clone(self, ref, git_cmd):
 # pragma: windows no cover """Perform a shallow clone of a repository and its submodules """


        git_config = 'protocol.version=2'
        git_cmd('-c', git_config, 'fetch', 'origin', ref, '--depth=1')
        git_cmd('checkout', ref)
        git_cmd(
            '-c', git_config, 'submodule', 'update', '--init',
            '--recursive', '--depth=1',
        )