Well, there
is actually an
ipconfig CLI command! (
man ipconfig tells you all about it.) The command
sudo ipconfig set en0 DHCP (case is important---'DHCP' not 'dhcp')
will do a DHCP lease renew, with all the attendant DNS renewing. I imagine that there is a more direct way to do what you want using
dscl, the Directory Services command line interface (again,
man dscl
for details).
What is the problem that you are you trying to solve?