How to clear file written after simulation cycle is over?

Hello,

I want to do this

1. Write the position of particles during the contact interaction step to a file
2. Use the positions written to compute particles with one ID up and One ID down to get the distances.
3. I want to clear the file written in Step 1 and re-write the file

I can achieve steps 1 and 2

But i do not know how to achieve step 3. Can someone please tell me how I can clear out the file so that I can write the particle positions again?