How to send output to a file continuously from a piped linux command?

Question

Below command generates output every second for 60 seconds.

sar -n DEV  1 60 | grep lo

If I redirect it to a file, the file sar.log is updated continuously i.e. every second

sar -n DEV  1 60 > sar.log &

However, as soon as pipe it and then redirect it to a file, it populates the file sar.log only after it has finished i.e. after 60 seconds.

sar -n DEV 1 60 | grep lo > sar.log &

How do I grep and redirect to a file so that the log file is updated continuously i.e. every second

I am ok with using something other than grep if it serves my purpose of selecting something and redirecting to a file every second.

Answer 1

With GNU grep: Add option --line-buffered to use line buffering on output. This can cause a performance penalty.