The s6-ftrig-listen program

s6-ftrig-listen subscribes to several fifodirs, then spawns a program, then waits for pattern of events to occur on the fifodirs.

Interface

In an execlineb script:

     s6-ftrig-listen [ -a | -o ] [ -t timeout ] { fifodir1 regexp1 fifodir2 regexp2 ... } prog...

s6-ftrig-listen subscribes to fifodir1 with the regexp regexp1, to fifodir2 with the regexp regexp2, and so on.
It then forks and exec prog... with all its arguments
It waits for the series of events received on fifodir-i to match regexp-i, The regexp-i must be Extended Regular Expressions.
When the series of read events matches the regexps, s6-ftrig-listen exits 0.

Options

-t timeout : if the events on the fifodirs have not matched the regexps after timeout milliseconds, print an error message on stderr and exit 1. By default, s6-ftrig-listen waits indefinitely for a matching series of events.
-a : and (conjunction). s6-ftrig-listen will only exit when all the fifodir-i have been notified with events matching the corresponding regexp-i. This is the default.
-o : one (disjunction). s6-ftrig-listen will exit as soon as one of the fifodir-i has been notified with events matching its regexp-i.

Notes

s6-ftrig-listen can be used outside of an execlineb script by using the internal argv syntax, but this syntax is an implementation detail and is not documented as stable. In a shell script, use execlineb -Pc 's6-ftrig-listen ...' to get the benefits of the execlineb brace syntax.