create a lock file in bash to avoid duplicate execution

Question

I'm not very good on bash I've been modifying a code to create a lock file so a cron don't execute a second time if the first process hasn't finish.

LOCK_FILE=./$(hostname)-lock
(set -C; : > $LOCK_FILE) 2> /dev/null
if [ $? != "0" ]; then
   echo "already running (lock file exists); exiting..."
exit 1
fi

trap 'rm $LOCK_FILE' INT TERM EXIT

when I run it for the first time I get the message already running as if the file already existed.

Perhaps I'm missing something

Answer 1

#!/bin/sh

(
  # Wait for lock on /tmp/lock

  flock -x -w 10 200 || exit 127 # you can use or not use -w

  #your stuff here

) 200> /tmp/lock

check man page flock.

This is the tool for you. And it comes with example in man page :)