send email from multi-lined grep output

Question

doesn't grab $ERROR and no email or killing the tail. what am i doing wrong?

tail -F --max-unchanged-stats=5 somelogfile.log | grep -B4 "FATAL" | while read ERROR
do
    echo $ERROR | mail -s 'FATAL ERROR' admin@someserver.com && pkill -P $$ tail
done

Answer 1

Add "--line-buffered" to the grep command. But as stated in the answer by @Nick, you will get an email for each line. May want to just remove the "-B4" argument from the grep command.

tail -F --max-unchanged-stats=5 somelogfile.log | grep -B4 --line-buffered "FATAL" | while 
read ERROR
do
    echo "$ERROR" | mail -s 'FATAL ERROR' admin@someserver.com
done

Try this. I tested on my CentOS 6.9 VM and I believe it does what you are looking to accomplish. When the script is first started, you may get a few emails if there are "FATAL" messages near the bottom of the log file.

#!/bin/bash

tail -f --max-unchanged-stats=5 somelogfile.log | grep --line-buffered "FATAL" | while read ERROR
do
    grep -B4 "$ERROR" somelogfile.log \
    | mail -s 'FATAL ERROR' admin@someserver.com
done 

Answer 2

tail and grep probably buffer stdout, so the while loop does not see it. If you have stdbuf (it should be available on Linux, but I'm not sure about other systems), try

stdbuf -o0 tail -F --max-unchanged-stats=5 somelogfile.log | stdbuf -o0 grep -B4 "FATAL" | while read ERROR ;do ... ;done

But there is another problem: The while read ERROR will read one line and assign it to ERROR each time around the loop. Your grep prints four lines before the FATAL line, so you'd be sending five emails, not one.