Split large file : Recordset per message

Hi experts,

I have a large file that I want to split: flat file -XI. This is an exemple of file :

HEADER;XYZ;123;123456

DETAIL;XYZ;123;123456

DETAIL;XYZ;123;123456

DETAIL;XYZ;123;123456

DETAIL;XYZ;123;123456

..

..

..

..

TRAILER;XYZ;123;456

Every splited file shoud contain 1500 of 'DETAIL' and also should contain the 'HEADER' structure.

Any idea ?

Cordialy,