tail -f

[Roberto Severo]

Hello,

I'm trying to use the following command:

tail -f log.txt | grep sql >> log2.txt

but the log2.txt file is aways empty, even if a line containing "sql" is stored in log.txt.

Can you help me? Is there other way to do that?

tks.

Roberto

[Pete Randall]

Roberto,

What I think you really want to do is:

tail log.txt |grep sql >> log2.txt


The -f option is the follow option.


Pete

[Paula J Frazer-Campbell]

Hi

What does
cat log.txt | grep sql >> log2.txt

give you?

Paula

[Bryan D. Quinn · Accepted solution]

Hello Roberto,

I know this will work:

tail -f log.txt | while read LINE
do
echo $LINE | grep sql >> log2.txt
done

I know it is a bit more than what you had, but it will work.

Hope this helps!
-Bryan

[DIPAK KUMAR ROY]

Try without "-f" option.

tail log.txt |grep sql >>log2.txt

Thanks

[Paula J Frazer-Campbell]

Hi
tail -n 10 log.txt |grep sql >> log2.txt

will do the last tem lines.

Paula

[Roberto Severo]

Pete,

What i want is to monitor the file log.txt, and as soon as a line with "sql" is appended, the file "log2.txt" is appended too. In other words, the file "log2.txt" is a online filter of the "log.txt".

Roberto

[Helen French]

You may need to try 'cat' command instead of tail:

# cat log.txt | grep sql >> log2.txt

tail command without a line option will list only the last 10 lines, but can increase that number with:

# tail -20 or tail -50 etc

[Michael Schulte zur Sur]

Hi Roberto,

if you setup a pipe command like you do, output of the grep will not immediately go to log2.txt. It stays in a buffer until enough is ready for output or the command responsible for the output ends and thereby a flush occurs. You should have immediately the text in the outfile, when you quit the command.

greetings,

Michael

[Pete Randall]

Roberto,

In that case, I think Brian's suggestion is more what you need.


Pete

[Bryan D. Quinn]

Hello Roberto,

I do the same thing with one of our logs and the lines I provided should handle that for you.

-Bryan

[DIPAK KUMAR ROY]

Try this...

while true
do
tail -n 1 log.txt | grep sql >> log2.txt
done



Thanks

[Paula J Frazer-Campbell]

Hi

create a file called checksql containing
----------------cut--------------
#!/bin/sh
cat log.txt | grep sql >> log2.txt
sleep 60
exec checksql
----------------cut-----------------

This will pick up all instances of sql and write it out to your log file, sleep for 60 seconds, and then rerun itself.

Paula

[Roberto Severo]

Paula/Dipak,

Your solutions would repeat the past occurrences.

Bryan,

I don't know why, but your solution did not work properly.

Roberto

[Michael Schulte zur Sur]

Hi Roberto,

try this:

#!/bin/ksh
LCOUNT=`wc -l log.txt|awk '{print $1}'`
while true
do
LCOUNT2=`wc -l log.txt|awk '{print $1}'`
if test ${LCOUNT} -eq ${LCOUNT2}
then
sleep 5
else
LINENUM=`expr ${LCOUNT2} - ${LCOUNT}`
tail -n${LINENUM} log.txt | grep sql >> log2.txt
LCOUNT=${LCOUNT2}
sleep 5
fi
done

[Bryan D. Quinn]

Hello Roberto,

When a line with sql is found in log.txt, then that entire line is appended to log2.txt? Is that correct?

If so, I am not sure why you had problems with my solution. I use it to tail our backup log every night. I just tested it again and as soon as log.txt is updated with a line with sql it is written to log2.txt.

What did you get when you tried it?

-Bryan

[Roberto Severo]

Bryan,

I think the problem was my "shell", now everything works fine!

You're 10!

tks

[Bryan D. Quinn]

Hello Roberto,

Good, glad it worked out!

Thanks,
-Bryan

[Michael Schulte zur Sur]

Hi,

I just found out, that my solution wasnt as waterproof as I thought, but who cares. The solution of Bryan is simple and ingeniuos. I still marvel, why it works. I spent many hours to find something like that because I wanted to controll "interactively" an ftp, but the last line of the output never showed up in the log. So I will have to try this one.

be happy,

Michael