Where is the buffer in this following ... and how do I turn it off?
I am writing out to stdout in a python program like so:
for line in sys.stdin:
print line
There is some buffering going on here:
tail -f data.txt | grep -e APL | python -u Interpret.py
I tried the following to shake off possible buffering ... with no luck:
used the following modified command:
stdbuf -o0 tail -f data.txt | stdbuf -o0 -i0 grep -e APL | stdbuf -i0 -o0 python -u Interpret.py
To benchmark my expectations, I tried:
tail -f data.txt | grep -e APL
This produces a steady flow of lines ... it surely is not as buffered as the python command.
So, how do I turn off buffering? ANSWER: It turns out there is buffering on both ends of the pipe.
file.readlines()
and for line in file
have internal buffering which is not affected by -u
option (see -u option note). Use
while True:
l=sys.stdin.readline()
sys.stdout.write(l)
instead.
By the way, sys.stdout
is line-buffered by default if it points to terminal and sys.stderr
is unbuffered (see stdio buffering).