Bash script lock file example

Learn more about clone URLs. Download ZIP. Bash flock example. This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters Show hidden characters. Copy link. Yours, Kindly, Val'. I don't have lockfile program on my linux, but one thing bothers me - will it work if first script will die without removing lock?

You should also use the trap builtin to catch any signals that might kill your script prematurely. Seems like a good package to use and mentions a "--use-pid" option. Show 6 more comments. Finally, the man page shows a nice example for multiple commands: flock -n 9 exit Jake Biesinger Jake Biesinger 4, 2 2 gold badges 22 22 silver badges 25 25 bronze badges.

I agree, flock is nice, especially compared to lockfile since flock is usually pre-installed on most Linux distros and doesn't require a large unrelated utility like postfix the way lockfile does. Cerin I need to do same thing with ffmpeg process conversion so i need to finish the first process regardless of crontab in every minute?

Use bash set -o noclobber option and attempt to overwrite a common file. A short example if! A longer example This example will wait for the global. One disadvantage of this as opposed to flock -style locking is that your lock isn't automatically released on kill -9 , reboot, power loss, etc.

If power loss is a concern, then using a temporary directory for the lock file would work, e. I still consider this approach generally less robust to anything where the kernel provides a guarantee of release. I'm not sure I follow why that's a concern; you can certainly grab a lock with a dynamic filename with flock after your program has started, and release it without exiting.

Using some modern bash 4. This solution is useful in my case where flock and lockfile are not available in the environment. Show 3 more comments. To unlock: dotlockfile -u file. James Tan James Tan 1, 1 1 gold badge 13 13 silver badges 28 28 bronze badges. I'm not sure there's any one-line robust solution, so you might end up rolling your own. Lockfiles are imperfect, but less so than using 'ps grep grep -v' pipelines. What is the 0 signal? It can't be seen in kill -l — qed. See gnu.

It looks much like the try However, when sending signal 0 with kill This is used for waiting polling for the end of one of your processes that is not the son of the current process. Signal 0 does not have any effect. Command "lsof" will do two advantages. Ignore pids which is editing by editor such as vim, because vim edit its mapping file such as ".

Isn't the purpose of lock is to hold up till the lock is released. Pocha that's one way it could work but you might equally want the script to exit with an explanation that's why I came here. If the behaviour described is what you desire it should be easily possible to modify this answer to achieve that. I hope this helps. I didn't say it was a duplicate, the intention was to point a relatively new user to search a little more thoroughly through S.

I looked for [bash] file lock and [bash] mutex and found numerous that would add perspective. Good luck. PSkocik PSkocik Massimo Thanks for pointing that out. I've addressed your point in an edit. Nice catch! Note that this needs bash 4. With local -n bash 4. It's just a demonstration of the mechanism. Sure you'd normally want your lock file somewhere else than in whatever the current directory happens to be.

If-Else statements allow the shell interpreter to make the correct decision based on several conditions. If the condition in the if statement is not met, then a block of code between else and fi will be executed before continuing with the rest of the script. A Loop allows you to run a series of commands a number of times until a particular condition is met.

While loops execute a block of code over and over as long as the condition is met. As soon as the condition is no longer met, the loop exits. Loops are very useful for automating repetitive tasks.

The loop iterates as long as n is less than or equal to 5 and prints the following output:. Save and close the file, then create a test-file. You can also check the existence of a file or directory using the -f and -d options in bash scripts. For example, create a test-check.

In this script, we also show you how to pass arguments to a script when calling it from the command line. Next, create another script named test-checkdir. These are just a few examples of some basic bash script concepts and syntax.