Flat file interface determination condition

hi All,

I have a scenario in which my sender sends a flat file and i need to check in the interface determination if the first four characters is the plant value. Based on that i need to route it to a different mapping.

I am aware of a solution in which we can use a basis receivers mappping in which we can set a variable binding which can be checked in the interface determination.

But I have seen a few cases like

"/p1:FlatFile/LIST[(starts-with(" XXXX"))]" in the condition with EX operator and empty on the RHS.

If we can use this, the effort would be much reduced. Please let me know how to do this in case of flat files if possible.

Regards,

Ninu