Run a command based on stdout frequency

Question

I have a program that writes to stdout in a batch of text very quickly, but the output doesn't have a specific output that I can write an expect loop for. Example of stdout of my program:

[time:here] random text 1
[time:here] random text 2
[time:here] random text 3
[time:here] random text 4
[time:here] random text 5
[time:here] random text 6
[time:here] random text 7

Then it waits until I interact with it, and then it writes to stdout again with the same style of text:

[time:here] random text 8
[time:here] random text 9
[time:here] random text 10
[time:here] random text 11
[time:here] random text 12
[time:here] random text 13
[time:here] random text 14

The stdout is printed very fast, like within milliseconds, and then there's a wait until I interact with it. Once I interact stdout is written again very quick, and it waits. This repeats until I close the program.

Between the waits I want to send a command to write to another file what time I interacted with the program at (using echo or something similar).

Is there any way I can target the "wait" and do the echo command after every time there's a wait for my stdout? For example if there's a wait for > than 5 seconds then run the echo command, and wait for stdout to change again?

Answer 1

You could use a blocking read with a timeout to determine when output has stopped. For example, Bash's read supports a timeout parameter. The following script will write a single line if the output from STDIN stops for more than 2 seconds:

#!/bin/sh

while read -r firstline; do
    while read -r -t 2 line; do
        continue
    done
    echo "---- No data in 2 seconds ----"
done

The echo could be re-directed to a different log and the script can be modified to echo the data being read from standard in if desired.