Create a txt file and name it thru macro

Hello,
I am trying to copy content of a worksheet to a text file. What i want to know is how can i name the text file based on a given string in a particular cell. And the issue is that i do not need the complete cell content I want to drop/trim last 4 characters of the cell.
Eg: value in my cell A1 is "abhimanyu_wk2" and i want to create a text file with name only
abhimanyu.
I need script to copy content to text file from a worksheet and name the text file based on the cell A1(as in the example given above).

Any help would be highly appreciated.

Thanks,
Abhimanyu