How to monitor only the last n lines of a log file?

Question

I have a growing log file for which I want to display only the last 15 lines. Here is what I know I can do:

tail -n 15 -F mylogfile.txt

As the log file is filled, tail appends the last lines to the display. I am looking for a solution that only displays the last 15 lines and get rid of the lines before the last 15 after it has been updated. Would you have an idea?

Thank you!

Answer 1

It might suffice to use watch:

$ watch tail -n 15 mylogfile.txt

Answer 2

You could stream the logfile running less and pressing SHIFT + F that will stream the file using less. $ less mylogfile.txt Then just press SHIFT + F and it will stream. I think it is convenient for monitoring log files that update.

Answer 3

If you use watch, try the -n option to control the interval between each update.

Thus, the following would call tail every 2 seconds

$ watch -n 2 tail -n 15 mylogfile.txt

while this one polls it every 1 second

$ watch -n 1 tail -n 15 mylogfile.txt

Answer 4

Maybe you find the -d param handy.

man watch

-d Highlight the differences between successive updates. Option will read optional argument that changes highlight to be permanent, allowing to see what has changed at least once since first iteration.