Shared File - How to input the collaborator user name when inputting data

Shared File - How to input the collaborator user name when inputting data

Hi,

I have created a file which is shared by a few collaborators.
The file comprises a few macros which upon clicking on a button will input rows of data from a source sheet to a target sheet. 
Assuming each row is comprised of 10 fields, u pon clicking this button, these fields will be populated in 10 target columns of the target sheet. 

I would like for this macro to populate an 11th column with the system username of the collaborator using the spreadsheet but can't find a solution.

Many thanks for your answer.