Start process and wait until logfile has specific entry

Question

I want to start a process in a bash script like this:

myProcess -p someparameter > log.txt &

And then I want to stop the process as soon as log.txt contains defined sentence to wait for. So I am NOT waiting for a file, but for an entry in a logfile!

What is the best way to do that (without frying my processors, hence no loops which run like crazy)?

Answer 1

In comments I expressed my concerns about the stability of such a solution because the process might already have been stepped further at the moment the watchdog detects the message in the logfile.

You said to that: The whole thing is about doing an automated analysis for one time on about 50 different inputs. Job done. It is not an academic exercise.

Ok, for such an use case you can do the following:

# Use stdbuf -oL to make sure the process output
# will get line buffered (instead of default block-buffered)
stdbuf -oL ./process -p param > logfile &
pid=$!

# Again make sure that the output of tail get's
# line buffered. grep -m1 stops after the first
# occurence
stdbuf -oL tail -f logfile | grep -m1 "PATTERN" && kill "${pid}"

Note: I suppose that process will exit nicely on kill in this example.