How to copy data from SalesOrderHeader /SalesOrderLine UDF column value in Shipment and Invoice UDF ?

Hi expert ,

    I have added 4/1 columns in SalesOrderHeader /SalesOrderLine / Shipment Header /Shipment Line  / Invoice Header /Invoice Line .

    I want to copy data from SalesOrderHeader /SalesOrderLine UDF column values to Shipment and Invoice UDF column when I have posted any Shipment / Invoice of a sales Order.

    Please give me suggession where I can write this code?

Thanks 

Surajit