I try to tail dmesg and pipe it to a file using watch:

i.e.
However, it is not formatted properly and the newline is removed in the tail_dmesg file (all became one line).

What is the proper way to do this?

Are you just trying to get the contents of the file in real time?
Cause the –c clears the buffer and then you write to a file with nothing there. The –f means to continually update on the screen – but then you use watch too?
Try doing:

If the previous reply doesn't solve your problem, then please clearly explain your goal. (Why are you doing this, and to what end?)

Thank you for your reply.

My goal is to get the contents of dmesg in real time from a remote linux PC and put them into a file on my local PC. Unfortunately my remote linux system is embedded and does not contain the file /var/log/dmesg. That is why I try to use watch. The option -c will display the content first then clear the buffer (i.e. always show the latest content in dmesg). Then I attempt to "watch" the latest content and put it to a file but failed.

The actual command I used is:
Sorry for not stating my goal clearly

I googled tail dmesg and found that you have answered a similar post in linux forums before! Unfortunately my linux system have limited disk space and does not contain /var/log/dmesg. It would be great if you can suggest me another solution

Try this :

That's nice, but my answer in that ~7 year old thread is (unfortunately) incorrect. Please explain - in plan English - the goal you're trying to achieve. We can make guesses based on the pipeline you've cobbled together, but the most elegant solution may present itself once we understand you better.

Also, what OS / version are you using?

Those are control codes to manipulate the cursor and clear the screen.
"watch" is designed to operate directly on the terminal and not be piped or redirected.

I had a normal local linux PC (any OS) and a remote embedded non-standard linux PC. My remote embedded linux PC has been customised with limited package and has limited disk space (that's why there is no /var/log/dmesg). Therefore, I proposed to retrieve the contents in dmesg from the remote linux PC (limited disk space) and put it in my local linux PC (plenty of disk space). In order to do that, I used ssh command and execute the dmesg/tail/... command to get the contents of dmesg and then watch/pipe it to a file on my local linux PC. So it will become something like this:

So I thought this command will ssh to remote_host and display the latest dmesg content(with -c option). So I watch this latest dmesg content and pipe it to the tail_dmesg file.

Hope now it is clear!

If your remote, embedded Linux box has syslogd installed, you might want to consider doing remote logging for kern.* (or whatever facility/level you want) messages instead. Something like that is arguably a better solution.

Example entry in syslog.conf(5):
Regular syslogd only does UDP (and clear text, for that matter), so bear that in mind if your link between the two hosts is unreliable.