How to automate if/else/then tasks in shell/bash in this context?

So to give context, let's say that I'm running a script that is creating a file with the title "name1.file", now I'm trying to figure how I would do this:

Execute the command, generate "name1.file", however if I was to run the command again, if "name1.file" is found, to generate "name2.file"- however I cannot figure out how to automate this process so it would continue on to name3.file, name4.file and vice versa...

How could this be achieved?

Using Ubuntu 16.04 server, this is a bash/shell script (.sh)