Hi Loong Chen,
Unfortunately there are no command line options to import source or target database definitions in the repository in PowerCenter. It is not possible to create source/target definitions using SQL file from the database using PowerCenter command. Currently, definition can be created using Designer client tool.
To export or import powercenter mapping pmrep objectimport command can be used.
What exactly do you plan to do? Could you please provide an example?
Maybe we can find a viable workaround together with you.