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=/usr/local/bin/gunicorn
ROOT=/path/to/project
PID=/var/run/gunicorn.pid

APP=main:application

if [ -f $PID ]; then rm $PID; fi

cd $ROOT
exec $GUNICORN -c $ROOT/gunicorn.conf.py --pid=$PID $APP

Google is useless in this case because searching for flags is useless

Answer 1

Google is useless in this case because searching for flags is useless

Fortunately, the Bash Reference Manual is available online, at http://www.gnu.org/software/bash/manual/bashref.html. It's the first hit when you Google for "Bash manual". §6.4 "Bash Conditional Expressions" says:

-f file

True if file exists and is a regular file.