CODEWITHSUNDEEP
bashgreppipetail
madsantos
madsantos

Reputation: 27

Bash- Running a command on each grep correspondence without stopping tail -n0 -f

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

Upvotes: 0

Views: 81

Answers (2)

Tomas Hrubovcak
Tomas Hrubovcak

Reputation: 355

use a while loop

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

Upvotes: 1

Eric Renouf
Eric Renouf

Reputation: 14520

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

Upvotes: 1

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