Working in HP-UX 10.20. I eventually want to write a bourne shell script to handle the following problem, but for now I am just toying with it at the command line.

Here's what I am basically trying to do:

tail -f log_X | grep n > log_Y

I am doing a tail -f on log_X . Once it sees "n", I would like for it to grep it, then put it into log_Y. It ain't making it to log_Y.

I have been manually adding "n" to log_X, and the tail command is definitely seeing it, but it fails to pass it to log_Y.

Why? Is it because the command is trying to "complete" the tail -f before it executes the > (redirect) to log_Y??

Is there a better way to appraoch this?

TYIA

try using

tail -f log_X | grep n >> log_Y

I'm not sure this would work...

I can add that the commands on either side of a pipe "|" are started and executed synchronously... and we know that any command like grep will finish only if it sees an EOF, which "tail -f" will not give as it is in an infinite loop looking for newly appended lines...

so...

tail -f log_X | grep n

should be working fine and giving "new" lines having "n" to stdout as and when they append to log_x...

It may be a problem with redirection, so use redirection in append mode >> and let us know!!

Cheers!
Vishnu.

Vishnu:

I tried using tail -f log_X | grep n >> log_Y yesterday...it DID NOT work. I also tried a tail -f log_X | grep n >! log_Y. No go.

The reason I am using tail -f is because I want this to be a "real-time monitor". Once "n" appears, I need it to notify me.

Any other ideas?

TYIA

see these posts.. it seems that piping "tail -f" works with some OSes and does not work with some...

http://www.computing.net/solaris/www...orum/1734.html

http://www.zsh.org/mla/users/1999/msg00360.html

you did not tell whether...

tail -f log_X | grep n

worked on your system.. i.e., you can see the stuff on your terminal..

Cheers!
Vishnu.

It seems that you would be better served to create a daemon to control this process.

You could tailor it to notify you when the string you want appears and email or beep you. You should have a template of one on your system or you can copy from a simple one in a directory similar to /sbin/init.d/template.

cp template myscript

You will need to add a kill and start link in your rc directories for it to startup a boot time.

ln -s myscript /sbin/rc3.d/S400myscript
ln -s myscript /sbin/rc1.d/K400myscript


Hope this helps!