Using tail -F to see a file changing in real-time

Question

I have a script that collects the size of a file that is being constantly fed. I'm echoing its size to a log file (echo 'filesize is $size' > log.txt) so I only have the last size information. So, only one line.

Now, in another terminal, I wanted to tail that log file to see its size increasing in real time. It turns out, tail -f path/to/file gives me the output I want but it keeps jumping to the next line (as expected, I guess).

So, the output is something like:

$ tail -F log.txt 2>/dev/null
filesize is 1.658 GB
filesize is 1.659 GB
filesize is 1.659 GB
filesize is 1.660 GB

I wanted something more like the command "less" in which you don't have the cursor back. Maybe a better example would be "mtr", that keeps updating the information on the screen without going to next line (as opposed to traceroute).

Thank you,

Answer 1

Use this command.

watch tail -n 1 log.txt

Answer 2

while [ 1 ]; do sleep 1; clear; tail log.txt; done

This does not have the drawback of passing command and arguments to watch (sometimes you need to hop extra loops to make it correctly), and it clears the terminal.