What does -f mean in bash

Question

I was looking at how to use runit to run gunicorn. I was looking at the bash file and I don\'t know what -f $PID does in

#!/bin/sh

GUNICORN=/us         


        

Answer 1

-f - file is a regular file (not a directory or device file)

Check this out for all file test operators: http://tldp.org/LDP/abs/html/fto.html