How to monitor for how much time each line of stdout was the last output line in Bash for benchmarking?

Question

For example, suppose I have the script:

(echo a; sleep 1; echo b; sleep 3; echo c; sleep 2)

which outputs:

a
b
c
         


        

Answer 1

If you're happy with a resolution of seconds, you can use this one-liner:

t=$SECONDS; (echo a; sleep 1; echo b; sleep 3; echo c; sleep 2) | while read line; do echo $((SECONDS - t)) $line; t=$SECONDS; done

If you are OK with installing node.js, this is exactly what gnomon does: