How do I stop tail command in script

Question

What I want to do - Start capturing the CHANGES to a log file using a custom ssh client code***. After some time (which not a fixed value and is event based), issue a command to stop tailing. This is the command I use to capture the latest changes to a log file - tail -f logfile.txt

I want to be able to end it with something like :q which I can issue from a script. I don't want to keyboard commands like ctrl + c.

*** Pseudo code for my custom ssh client code (written in an oop language)

include ssh-api
ssh = getSSHConnection();
cmd = 'cd to folder';
ssh.command(cmd);
cmd = 'tail -f log.txt';
ssh.command(cmd);
wait for special event to occur...
cmd = 'stop the tail now!'
out = ssh.command(cmd);
print "the changes made to log file were\n"  + out;

I have no write access to the server where the log file is located.

What I tried - http://www.linuxquestions.org/questions/red-hat-31/how-to-stop-tail-f-in-scipt-529419/

I am not able to understand the solution there (Its in post 2). Can someone please explain the solution or suggest a different way to do this?

Thank you.

Answer 1

Inside your script you can make use of $! variable.

# run tail -f in background
tail -f /var/log/sample.log > out 2>&1 &

# process id of tail command
tailpid=$!

# wait for sometime
sleep 10

# now kill the tail process
kill $tailpid

$! Expands to the process ID of the most recently executed background (asynchronous) command.