How can I run a particular script every second?

Question

I have tried using crontab, but it is limited to minutes. Is there any other option?

I have also tried something like:

watch -n 1 sh /path-to-script/try.sh

But whenever I close the terminal it stops. I want something which continuously works in the background.

Solution

Use a script with the while loop and nohup.

the_script.sh:

while :; do
  /path-to-script/try.sh
  sleep 1
done

Run the_script.sh immune to hangups:

nohup /path/to/the_script.sh > /dev/null

Replace /dev/null with some file path if you care what's in the stdout.

Comments

[George Vasiliou]

I would focus on using & at the end of the command and also would read some about disown and nohup - see here for details unix.stackexchange.com/questions/3886/…

[ilkkachu]

Starting every second or starting a second after the previous one stopped? The latter is trivial, the first is a bit tougher. In the first case, you'd also want to consider what to do if one invocation takes longer than a second for some reason.

[Prashant Luhar]

actually its a script to check if MySQL daemon is running or not... so script takes less than a second to execute.

[Prashant Luhar]

I read about disown and nohup. So if I destroy the terminal on which the script is running it will destroy the program as well. @GeorgeVasiliou

[Thegs]

@PrashantLuhar not with nohup, no. Using nohup [command] & makes the command ignore the terminal's attempts to kill child processes upon the terminal's logout.

[XPMai]

I recommend using that command in conjunction with screen, see: linux.die.net/man/1/screen

[Prashant Luhar]

Actually I have tried this too, but whenever I close the terminal it terminates the script..so the real problem here is how to run the script in background. And yes if its not running I send an email using mailx command

[TheNH813]

Put the script code in ~/.local/bin/notifymysqldown or /usr/bin/notifymysqldown and add it to one of the login startup scripts like this "notifymysqldown&". Whenever you log in the command will execute, in the background without a terminal window. To kill it off you'd need to open a task manager and look for notifymysqldown.sh and end it. You'd also want to add a if then else section so the script pauses a few minuted if it does go down so it doesn't send a email every second.

[Bruce]

Run this bash script in background, like ./script.sh &, and then run command disown, then you can safely close your terminal. Another way is using screen.

[Prashant Luhar]

I did the same thing. It is running perfect... Thanks for the help ;)