How can I check a file exists and execute a command if not?

Question

I have a daemon I have written using Python. When it is running, it has a PID file located at /tmp/filename.pid. If the daemon isn\'t running then PID file doesn\'t exist.

Answer 1

If it is bash scripting you are wondering about, something like this would work:

if [ ! -f "$FILENAME" ]; then
   python daemon.py restart
fi

A better option may be to look into lockfile