excel spreadsheet macro

I need help with trying to automate columns of a spreadsheet. For example I am needing to name each row that has existing data. On some excel documents I need to number automatically to 30 and on others I only need to name 10 and on others maybe 20, Here is an example


job1
job2
job3
job4
job5
job6
job1
job2
job3
job4
job5
job6
 
I would like to be able to select each row and have this automated

job1
job2
job3
job4
job1
job2
job3
job4
job1
job2
job3
job4

Over and over again until the last row with data. I appreciate any type of help thanks