Bash flock example

bash_flock.sh

#!/bin/bash
#
# Bash `flock` example.
# Works on: Linux, BSD
# Doesn't work on: MacOS

# The file which represent the lock.
LOCKFILE="`basename $0`.lock"

# Timeout in seconds.
TIMEOUT=2

# Create the lockfile.
touch $LOCKFILE

# Create a file descriptor over the given lockfile.
exec {FD}<>$LOCKFILE

# Try to lock the file descriptor $FD during $TIMEOUT seconds.
# If it failsm exit with an error.
# Otherwise, the lock is acquired and implicitely droped at the end of the script.
if ! flock -x -w $TIMEOUT $FD; then
  echo "Failed to obtain a lock within $TIMEOUT seconds"
  echo "Another instance of `basename $0` is probably running."
  exit 1
else
  echo "Lock acquired"
fi

Stumbled upon this by accident. Here's the answer to the question:

https://unix.stackexchange.com/questions/226164/what-does-exec-fd-dev-watchdog-do-in-bash

also found flock man page