I have discovered that if I type the ping x.x.x.x or hostname interface command and press tab for completion after interface an error is displayed:
vyos@gateway:~$ ping 8.8.8.8 interface Traceback (most recent call last):
File "/usr/libexec/vyos/op_mode/ping.py", line 258, in <module>
result = options[matched[0]]['helpfunction']()
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3/dist-packages/vyos/utils/network.py", line 205, in interface_list
return Section.interfaces()
^^^^^^^NameError: name 'Section' is not defined
Possible completions:
<Enter> Execute the current command <text> Ping options