code: def _get_login_shell(proc_cmd):
      
      login_shell = os.environ.get('SHELL', '')
      if login_shell:
          proc_cmd = login_shell
      else:
          proc_cmd = proc_cmd[1:]
      return (os.path.basename(proc_cmd).lower(), proc_cmd)
docs: Form shell information from the SHELL environment variable if possible.