There is no good way to repeat a prep stanza if it failed

[dottedmag]

prep stanza runs once and stops the block if it failed.

This is most often what one needs, but sometimes prep failures are transient: e.g. a script was unable to apply DB schema while PostgreSQL server is starting. In this case it would be nice to repeat prep until it succeeds.

I have tried wrapping prep stanzas in while ! x; do sleep 1; done, but this solution also has issues:

• It does not back-off
• It is a separate shell script that will continue to run if ppow is brutally killed.

So, what I need is a hybrid between prep (run before other commands, allow other commands to run if prep succeeds) and daemon (rerun with backoff).