Force a shell script to fflush

Question

I was wondering if it was possible to tell bash that all calls to echo or printf should be followed up by a subsequent call to fflush()

Answer 1

If comands use stdio and are connected to a terminal they'll be flushed per line. Otherwise you'll need to use something like stdbuf on commands in a pipe line http://www.pixelbeat.org/programming/stdio_buffering/

tl;dr: instead of printf ... try to put to the script stdbuf -o0 printf .., or stdbuf -oL printf ...

Answer 2

Maybe "stty raw" can help with some other tricks for end-of-lines handling. AFAIK "raw" mode turns off line based buffering, at least when used for serial port ("stty raw < /dev/ttyS0").

Answer 3

If you force the file to be read, it seems to cause the buffer to flush. These work for me.

Either read the data into a useless variable:

    x=$(<$logfile)

Or do a UUOC:

    cat $logfile > /dev/null