I want to get only the number of ms from a ping command to a file Without piping to a file it works as intended. I'm a little bit lost on why > to a file does not write anything.
This works:
ping 192.168.1.1 |egrep --line-buffered -v 'PING|timeout' |sed -l -e 's/^.* time=\(.*\) ms$/\1/g'
This does not write anything to ping.dat
ping 192.168.1.1 |egrep --line-buffered -v 'PING|timeout' |sed -l -e 's/^.* time=\(.*\) ms$/\1/g' > ping.dat
What am I doing wrong?
Each | is potentially surrounded by an stdio output buffer and an stdin input buffer. You need to find out which of those you need to turn off to get realtime piping.
This works for me:
ping localhost |egrep --line-buffered -v 'PING|timeout' |\
stdbuf -o0 sed -l -e 's/^.* time=\(.*\) ms$/\1/g' > file
Initially I had put stdbuf -i0 -o0 before every command and then found out which were unnecessary.
If you're using GNU, then it appears the -l option to sed is incorrect: you probably want the -u (unbuffered) option. Also, the grep is superfluous. You should be able to get what you want from just the sed:
ping $HOST | sed -u -n '/ ms$/s/.* time=\(.*\) ms$/\1/p' >file.out
The -n suppresses normal matching output, while the s///p forces the output of matching lines.
--line-bufferedwith egrep solve this? Or does grep's output then also get buffered? – Otheus Feb 16 '16 at 13:56stdbuf -o0does solve the problem, it appearsseduses stdio and the stream gets stuck in itsstdout's output buffer. – Petr Skocik Feb 16 '16 at 14:04-ualso does this. – Otheus Feb 16 '16 at 14:22