UNIX for Dummies Questions & Answers

Hi,
My program A updates a log called logA.

I have a shell script S that is responsible to send emails reading from the log.
I want to trigger execution of the script whenever there is an update to the log.

Thanks in advance.

If you have no control of the process that writes to the log file, one approach would be the following:

a) Create a script to determine if something has happened to the log file. You might look at the last modification date/time or the number of lines in the log file.
b) This script will need to save what it last knew (to a file probably) for comparison.
c) Will need to setup this script as a cron job - running as often as you believe necessary. Do you need to know the second a log entry is made, or is hourly sufficient? The more precise you need to know, the more computer resources will be taken to determine it.
d) When script found a new entry, create your email message and use mailx or mutt or other email to send notification.

if logA is dedicated to Script A means, we can make it simple.

Whenever the Script A writes to the log file.after that line call the script S to send email.

hi ,
i dont know whether i understood correctly ,

if there is an update in a log-file then u want to run a shell-script [which does something ] !!

i will do this in a simple way by running a deamon-job which keeps checking the log if increase in size then run the script S

>>>>>>>>>>>>>>
prev-size= [get the size od the file ]
start-loop
current size =[get the size of the file]
if current-size > prev-size then
execute shellscript S
else
continue
fi
end-loop
<<<<<<<<<<<<<<<<<

but this will be like writing another shell-script , i dont know is it useful 4 u or may b ur looking for some simple command for triggering

UNIX and GNU/Linux do not have a builtin general purpose event mechanism/API that you could use to monitor a log file and perform actions depending on the contents of the log file. However there are any number of log monitoring utilities available. Just do a search on the Internet for "Linux watch log files"

unfortunately, CRON is out of question due to security issues. its the company standard.

actually the log is not updated quite often, however, the requirement is to get the notification as soon as there is an update.. few mins here & there is not an issue at all.

but Program A is totally dedicated to doing something else.