How to clear contents of a file without deleting it.

Hi,

I have a script which will use an input.txt file as an input file.
I am providing data to this input file in the script and once the script is executed, I want to clear all the contents of this file as during the second time use of this script, I'll be appending the data in this input file.

So basically I want to know a way using which I can just clear all the contents of the file input.txt and make it a blank file. Like one which is just created with no data in it.
Can this be done.

Thanks in advance!