bash script: repeat command if it returns an error

Question

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

Answer 1

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

Answer 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

Answer 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

Answer 4

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;