Home / server / Questions / 80862
Accepted
Roy
Asked: 2009-11-04 01:05:19 +0800 CST

bash script: repeat command if it returns an error

  • 772

I would like to create a loop that repeats a ncftp transfer if it returns an error.

I'm a little unsure how the exit code variable can be used in a loop. Would something like this work?

until [$? == 0]; do
    ncftpput -DD -z -u user -p password remoteserver /remote/dir /local/file
done
bash

6 Answers

  1. Best Answer

    I found the basis for this elegant loop elsewhere on serverfault. Turns out there is no need save the exit code, as you can test directly on the command itself;

    until ncftpput -DD -z -u user -p password remoteserver /remote/dir /local/file; do
  echo Tansfer disrupted, retrying in 10 seconds...
  sleep 10
done
    • 60

  2. Almost. You are probably better saving the return value as a variable so that you can pre-set it before the loop. Otherwise it will be affected by the last-run command.

    You might also want to sling a sleep in there to stop it respawning too quickly.

    RET=1
until [ ${RET} -eq 0 ]; do
    ncftpput -DD -z -u user -p password remoteserver /remote/dir /local/file
    RET=$?
    sleep 10
done
    • 11

  3. Bit hacky but my solution was to just create a bash function which runs itself if it exits with a failure

    function retry { the_command_you_want && echo "success" || (echo "fail" && retry) }; retry
    • 5

  4. Some of the solutions shown on this page will loop an infinite number of times if the command continues to fail.

    If you're not a fan of infinite loops try this:

    function retry {
    command="$*"
    retval=1
    attempt=1
    until [[ $retval -eq 0 ]] || [[ $attempt -gt 5 ]]; do
        # Execute inside of a subshell in case parent
        # script is running with "set -e"
        (
            set +e
            $command
        )
        retval=$?
        attempt=$(( $attempt + 1 ))
        if [[ $retval -ne 0 ]]; then
            # If there was an error wait 10 seconds
            sleep 10
        fi
    done
    if [[ $retval -ne 0 ]] && [[ $attempt -gt 5 ]]; then
        # Something is fubar, go ahead and exit
        exit $retval
    fi
}

    Now, whenever you need a retry loop, just run:

    retry mycommand and args

    e.g.:

    retry ncftpput -DD -z -u user -p password remoteserver /remote/dir /local/file
    • 3

  5. You can do a loop while your command returns error:

        while [ -n $(ncftpput -DD -z -u user -p password remoteserver /remote/dir /local/file) ]; do
            sleep 1;
    done;
    • 1

  6. I've had a similar problem with needing to repeat curl requests, and the scripting was getting out of hand. As a result I created the retry tool:

    retry ncftpput -DD -z -u user -p password remoteserver /remote/dir /local/file

    In this case, the ncftpput command will be retried indefinitely until it returns a success status code, backing off by default for ten seconds in between.

    Retry is available here: https://github.com/minfrin/retry

    • 1