Bash-在每个grep对应关系上运行命令，而不停止tail -n0 -f

Question

I'm currently monitoring a log file and my ultimate goal is to write a script that uses tail -n0 -f and execute a certain command once grep finds a correspondence. My current code:

tail -n 0 -f $logfile | grep -q $pattern && echo $warning > $anotherlogfile

This works but only once, since grep -q stops when it finds a match. The script must keep searching and running the command, so I can update a status log and run another script to automatically fix the problem. Can you give me a hint?

Thanks

Answer 1

use a while loop

tail -n 0 -f "$logfile" | while read LINE; do
    echo "$LINE" | grep -q "$pattern" && echo "$warning" > "$anotherlogfile"
done

Answer 2

awk will let us continue to process lines and take actions when a pattern is found. Something like:

tail -n0 -f "$logfile" | awk -v pattern="$pattern" '$0 ~ pattern {print "WARN" >> "anotherLogFile"}'

If you need to pass in the warning message and path to anotherLogFile you can use more -v flags to awk . Also, you could have awk take the action you want instead. It can run commands via the system() function where you pass the shell command to run