How can call an external program(non-sap) from ABAP/4

Hi Experts,

I want to call an external program in a non-sap system from our ABAP program. The simple business senario is:

User create/change a objects, for example, vendor master/internal order, etc, once he/she press the SAVE button then the program will call the external program to update the same data in the counter-system(Supposed we have an user-exit is available for the SAVE button).

I had ask my friends on this topic and they tell my that we can set an external command in SM69, and then call the function module SXPG_COMMAND_EXECUTE to triger the external program. But I do not understand that how we set the import/export parameters for the external program?

And how the external program received my parameters? And how I can set the destination for SXPG_COMMAND_EXECUTE.

Do any experts had an idea on this topic, Please kindly point me a direction. Thanks very much in advance.