Stream to stdout while running instead of waiting for runitor to exit

[daviewales]

Currently, if I run something like the following, I don't see output in the log file until the process completes:

runitor -- example-script | ts >> /var/log/example-script.log

For example, I might want to run tail -f /var/log/example-script.log in another window to check the progress.

Would it be possible for runitor to stream output from the wrapped command to stdout, rather than buffering until the process completes?

[bdd]

Are you sure your example-script is actually flushing its output?

You can try this one as a proof to see how runitor does not hold on to the output as you described above.

runitor -- sh -c 'for i in {1..10}; do echo $i; sleep 1; done' | ts

In this example above, your shell will be piping runitor's output.

[daviewales]

Thanks! Hmm... You are correct, that does work as expected (after changing sh to bash).

I'll check my script.

[daviewales]

For future reference, my example-script was a Python script, and it seems that Python buffers the output of print() by default.

This doesn't print anything until the end:

runitor -- python3 -c 'for i in range(10): import time; print(i); time.sleep(1)' | ts >> test-runitor-output

But this does:

runitor -- python3 -c 'for i in range(10): import time; print(i, flush=True); time.sleep(1)' | ts >> test-runitor-output

[bdd]

...or you can pass -u to Python.

e.g.

#!/usr/bin/env python3 -u

...and if you find yourself in a situation where modifying the script isn't possible or desirable, you can pass it directly to python like python3 -u ./stubborn-thing.py overriding the interpreter along with the flags and args specified in the shebang.