Execute command when line matches

pgb205 · 07-18-2012, 10:56 AM

I'm monitoring a file with tail -f

tail -f <filename> |grep <string>

what i want to do is to execute another script when grep finds a new match.

Is there an event message that can be captured or some other method?

pixellany · 07-18-2012, 11:05 AM

Code:

if grep <string> filename 1>/dev/null; then
     <do stuff>
fi

chrism01 · 07-18-2012, 08:44 PM

Unfortunately, this seems to be an ever growing log file, so I don't think that would work because you'd have to know where you got to last time, then loop round and continue from that line num (not to mention logrotate issues).
I'd use http://search.cpan.org/~mgrabnar/Fil...0.99.3/Tail.pm instead, which is designed especially for this situation.

dru8274 · 07-18-2012, 11:45 PM

Perhaps something like this...

Code:

while IFS= read var ; do

    # Some script here to parse the line stored in $var

done < <(tail -f tailfile | grep 'some pattern here')

Kenhelm · 07-19-2012, 02:29 AM

This is working on my system using GNU grep.

Code:

tail -f <filename> | grep --line-buffered <string> | while read;do
                                                       <scriptname>
                                                     done

Without the '--line-buffered' option the matched lines would be held back in a buffer instead of being sent immediately through the pipe to the while loop.

David the H. · 07-20-2012, 11:38 AM

Or you could eliminate grep entirely.

Code:

while read -r; do

	[[ $REPLY == *string* ]] && ./scriptname

done < <( tail -f file )