Redirect to a different page based upon Variables in URL

Hi there. I’ve tried to find this to no avail. I am looking to create one landing page that will direct to different ones based upon a variable in the URL. For example:

http://XXXX.com/?vendor=VendorA would automatically go to:
http://XXXX.com/vendorA

and
http://XXXX.com/?vendor=VendorB would automatically go to:
http://XXXX.com/vendorB

Thanks!