Material Master Extract with some fields in legacy shorter then SAP

Hi ,

I need to Extract Material master data and send to Material Management System(MMS), i am able to fetch the data into internal table with fields of MMS structure. My problem is SAP has 18 characters for MATNR field and MMS has only 6 characters, like wise some fields are shorter length in MMS then in SAP. How can i truncate all the values of the corresponding fields in my output internal table so that i can download the file to MMS system.

Regards

Krishna