How to get the number of vbap records in VOFM-RV50B901

Hi Experts,

Please help me to find out the number of records of VBAP when i run VL01N.

Details:

Task: I have to do some validations based on the number of line items in VBAP.

As is Process

a.) I run VL01N with Item from 10 to 20 for a VBELN = 10000561.

b). Now in the RV50B901,i am by validating the number of CVBAP records against the database VBAP records

CVBAP has 4 records with posnr = 10,11,12,20

VBAP has 6 records with posnr = 10,11,12,20,21,22

d.) To get the all line items,I am using a select on VBAP table using VBELN = 10000561.

To-be Process Replace the select query ,if you get the number of records from any global variable/table

Thanks in advance

Lakshmi