Often I'll do something like

    long_running_thing | tee long_running_thing_stdout

and want to see the first few lines of output before going to do something else. The pipe causes buffering on stdout, though, so I have to sit there until 4k of output has come out on stdout.

As seen on https://unix.stackexchange.com/questions/25372/turn-off-buff... , either `unbuffer long_running_thing` or `stdbuf -oL long_running_thing` causes it to output linewise instead of 4k at a time.