tail and grep together

[peterneve]

I need to write a simple script that reads a continuous live log file, and if I find a particular string, write the next line to another log file. I've tried vaiour tail -f | grep combinations. This should be simple, but I can't get it so work. Any ideas?

 

[PHV]

tail -f seems to be a good starting point.
What have you tried so far ?

Hope This Helps, PH.
Want to get great answers to your Tek-Tips questions? Have a look at FAQ219-2884 or FAQ181-2886

 

[peterneve]

tail -f largelogfile | grep something >> newlogfile

doesn't seem to produce anything in newlogfile. Even this would be a start.

 

[peterneve]

I have also tried

tail -f largefile | awk '/something/{getline;print}' >> 
newfile

which produces nothing, although it works without the -f.

Thanks,

 

[hoinz]

Try without output redirection >> newlogfile
I guess this will work.
It seems to be a problem of output buffering.

 

[hoinz]

by the way, may I ask if there are situations where you really need both -f and redirection?
If you want to see it in real time, leave away redirection.
If you need it afterwards, do a grep afterwards, leave away tail.

 

[Annihilannic]

Yes, I have had similar problems with tail -f into an awk script, it seems to be buffering either the output from tail or the input to awk.

I had to replace my awk script with a perl script, and used the code described in the open section on the perlfunc man page to make STDOUT unbuffered.

I don't know why making STDOUT unbuffered fixed the problem (I would have thought it should be STDIN), but it did.

Annihilannic.