You can obtain a pretty decent amount of information about leases your OS X computer gets just by looking in the Network System Preference pane, for each interface.
However, you can get a little lot more information, as with most things, from the command line. First, we’re going to take a look at en0 on our host and see what the MAC address is:
ifconfig en0 ether
Now, we can look in the /var/db/dhcpclient/leases directory to see a list of all of the leases we have running on our system. Based on the MAC address of our computer, we should see a file there that starts with the name of our interface and finishes with our MAC address. Let’s cat this file:
The output is similar to the following (a standard plist):
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
This shows us the amount of time our lease is valid for, when the lease what provided to us, what IP was provided and the IP of our router. We can then key off of that information as needed (e.g. for other scripts/tools).