Re: infinite loop that is possible to quit

[Alex Satrapa <grail@xxxxxxxxxxxxxx>]

There's no real "good" or "bad" decision here until you start doing stuff inside that loop. How will immediately halting processing of that script cause trouble later? Will you corrupt data? Leave a peripheral in an unknown state? If there's no concern about data corruption, allowing Ctrl+C (or SIGTERM) terminate the processing of the script is fine.

Other options include:

1. Reading user input and looking for eg "q" being pressed
2. Looking for a specific file on the file system, eg ".stop" and stopping when that file appears
3. Looking for a specific file on the file system, eg "config" and stopping when that file disappears
4. Using a settings file which you watch for changes, reread the settings, and get the stop/go from a config settings
5. Catching Ctrl+C (SIGTERM) and handling it (more about that later)

    #!/bin/zsh
    
    CONTINUE=1
    
    wrap_up() {
        echo "Wrapping up."
        CONTINUE=0
    }
    
    trap 'wrap_up' HUP INT QUIT TERM
    
    while [ $CONTINUE -eq 1 ] ; do
        echo "I'm still here."
        sleep 5
    done

Which will produce something like:

    [user@host]$ ./traptest
    I'm still here.
    I'm still here.
    ^CWrapping up.

The traps I'm catching there are the ones usually associated with a soft shutdown.

HTH
HAND

> On 1 Dec 2020, at 12:50, Emanuel Berg <moasenwood@xxxxxxx> wrote:
> 
> How do I do an infinite loop that runs something, but it will
> still be possible to quit the whole thing?
> 
> The best thing I've come up with is
> 
> while true; do
>  # run program
>  sleep 1
> done
> 
> Then do, say, q to exit the program, and C-c during the sleep
> period to quit the loop!
> 
> Is this good or bad?
> 
> TIA
> 
> -- 
> underground experts united
> http://user.it.uu.se/~embe8573
> https://dataswamp.org/~incal
> 
>