How to retry a command in Bash?

I liked @Jonathan's answer, but tried to make it more straight forward for future use:

until timeout 1 sleep 2
do
    echo "Happening after 1s of sleep"
done

I found a script from: http://fahdshariff.blogspot.com/2014/02/retrying-commands-in-shell-scripts.html

#!/bin/bash
 
# Retries a command on failure.
# $1 - the max number of attempts
# $2... - the command to run

retry() {
    local -r -i max_attempts="$1"; shift
    local -i attempt_num=1
    until "$@"
    do
        if ((attempt_num==max_attempts))
        then
            echo "Attempt $attempt_num failed and there are no more attempts left!"
            return 1
        else
            echo "Attempt $attempt_num failed! Trying again in $attempt_num seconds..."
            sleep $((attempt_num++))
        fi
    done
}
 
# example usage:
retry 5 ls -ltr foo

Look at the GNU timeout command. This kills the process if it has not completed in a given time; you'd simply wrap a loop around this to wait for the timeout to complete successfully, with delays between retries as appropriate, etc.

while timeout -k 70 60 -- my_command; [ $? = 124 ]
do sleep 2  # Pause before retry
done

If you must do it in pure bash (which is not really feasible - bash uses lots of other commands), then you are in for a world of pain and frustration with signal handlers and all sorts of issues.

---

Please expand on your answer a little. -k 70 is --kill-after= 70 seconds, 124 exit on timeout; what is the 60?

The linked documentation does explain the command; I don't really plan to repeat it all here. The synopsis is timeout [options] duration command [arg]...; one of the options is -k duration. The -k duration says "if the command does not die after the SIGTERM signal is sent at 60 seconds, send a SIGKILL signal at 70 seconds" (and the command should die then). There are a number of documented exit statuses; 124 indicates that the command timed out; 137 that it died after being sent the SIGKILL signal, and so on. You can't tell if the command itself exits with one of the documented statuses.