tail -f into grep into cut not working properly
bash, cut, grep, shell, tail
Solution
the problem is almost certainly related to how grep and cut buffer their output. here's a hack that should get you around the problem, though i'm sure there are prettier ways to do it:
tail -f /var/somelog | while read line; do echo "$line" | grep "some test and p l a c e h o l d e r" | cut -f 3,4,14 -d " "; done
(don't forget the `; done` at the end of the command)
alternatively, because `gawk` doesn't buffer it's output, you could use it in place of `cut` to avoid the cumbersome while loop:
tail -f log | grep --line-buffered "some test and p l a c e h o l d e r" | gawk '{print $3,$4,$14}'
check out http://www.pixelbeat.org/programming/stdio_buffering/ for more info on buffering problems.
Problem
i'm trying to build a shell script to monitor some log files. I'm using a command like this: ``` tail -f /var/somelog | grep --line-buffered " some test and p l a c e h o l d e r" | cut -f 3,4,14 -d " " ``` the log file is like: ``` some test and p l a c e h o l d e r 3 some test and p l a c e h o l d e r 4 some test and p l a c e h o l d e r 5 some test and p l a c e h o l d e r 6 ``` and so on.. My issue is that the output of the command does not display the last line ``` some test and p l a c e h o l d e r 6 ``` until line ``` some test and p l a c e h o l d e r 7 ``` is added to the log. I hope I made clear my issue. Can anyone help me to solve this? Thank you :)