UNIX for Dummies Questions & Answers

I am trying to use this script however it is not running well

Code:

#!/bin/sh
tail -f filename | grep -i -E 'error|warning'

the code does not display the first 10 lines of the file that I want to check
since after the file grow, it cannot grep "warning" as well

Code:

#!/bin/sh
A=`tail -f filename | grep -i -E 'error|warning'`

the code does not display anything.


can someone please comment?

tail -f is a continous tailing of a file and not displaying the 1st 10 lines of a file. That would be a simple

Code:

head # defaults to 1st 10 lines

or

Code:

head -10

Also files usualy grow at the end of the file so you might want to be more precise if you want to check the latest 10 rows of a file or the 1st.

Rest of the grep is ok - but if it doesn't print anything it seems there is nothing in your file that matches.

The tail -f into a variable does not work since the defining of the variable does not end becuase the file you are tailing is kept open.
If you tell us what you want to do with the results inside a variable we can maybe show an alternative.

I want to put `tail -f filename | grep -i -E 'error|warning'` into a variable and construct an e-mail that report any lines that contain "error" or "warning", after that, I will send the mail to the address specified in the RECIPIENT shell variable which is defined within the script.

I have tried `tail -f filename | grep -i -E 'error|warning'` in the terminal, there is no problem that it displayed last(sorry it is not the 'first' I just posted) 10 lines of the file which contain "error" and "warning" firstly, and then wait for the file to grow and check the next line if it is contain the keywords.

also , the `grep -i -E 'error|warning'`, is it correct that it can grep all the "error" or "warning" in any combination of upper and lower case letters?

Thanks!

1. Yes the grep command which you had given and explanation are right.

2. you cannot use tail -f, use just tail.

Why did you want to use -f ?!

I use tail -f because the file the script check will grow, the task is to handle the growing content in the file.
but since using tail -f is not wise because I have no idea how to put it in to a variable.

A little shell script for the background:

Code:

$> cat logit.ksh
#!/usr/bin/ksh

LOGFILE=somefile

tail -f $LOGFILE| while read LINE; do
        echo $LINE| grep -q error && echo "`date` -- Error in [${LOGFILE}]!"| mail -s "Logfile warning!" you@bla.com
done

exit 0
$>
$> nohup ./logit.ksh &

If you want a bit more professional, check out swatch:
swatch: Automated Log Monitoring for the Vigilant but Lazy | Linux Journal