GIMP 1.0 has a batch mode that allows a limited subset of pdb commands to be started and ran from the command line, without or without the ui. It's there, and it works, but its certainly a little odd. This how-to is to help smooth out some of those rough spots.
This is primarily aimed at people wishing to learn how to setup gimp to use Script-Fu in a non-interactive manner. Script-FU is distributed with the gimp and includes lots of example scripts, so this how-to concentrates on it. It is possible to use batch mode to launch scripts from other language bindings, such as gimp-perl, gimp-tcl, etc. Those packages should have more info on that.