Terminating an infinite loop

Question

I have a command that I want to have run again automatically each time it terminates, so I ran something like this:

while [ 1 ]; do COMMAND; done;

but if I can't stop the loop with Ctrl-c as that just kills COMMAND and not the entire loop.

How would I achieve something similar but which I can stop without having to close the terminal?

Answer 1

Check the exit status of the command. If the command was terminated by a signal the exit code will be 128 + the signal number. For example if you interrupt a command with control-C the exit code will be 130, because SIGINT is signal 2 on Unix systems. So:

while [ 1 ]; do COMMAND; test $? -gt 128 && break; done

Answer 2

I generally just hold down Ctrl-C. Sooner or later it'll register between COMMAND's and thus terminate the while loop. Maybe there is a better way.

Answer 3

I would say it might be best to put your infinite loop in a script and handle signals there. Here's a basic starting point. I'm sure you'll want to modify it to suit. The script uses trap to catch ctrl-c (or SIGTERM), kills off the command (I've used sleep here as a test) and exits.

cleanup ()
{
kill -s SIGTERM $!
exit 0
}

trap cleanup SIGINT SIGTERM

while [ 1 ]
do
    sleep 60 &
    wait $!
done

Answer 4

If you run bash with -e it will exit on any error conditions:

#!/bin/bash -e
false # returns 1
echo This won't be printed