How to save specific command's kernel message

My question is about following URL: Cannot redirect "iwpriv show" command's output to text file

As up there, i already know that iwpriv command is not used for a long time.
However, that's the only way to make my apcli interfaces active.

Anyways,
iwpriv [interface] show [parameter] command prints its message at kernel message, so i can check it by accessing /proc/kmsg.

However, if i am right, accessing to kmsg is not a great idea. It does not ends until i quit, and only one process can access to that, so any other things cannot access while i am reading with cat command.

I considered using dmesg, which prints the kernel messages at my console, so i can use > log.txt to save kernel messages. Since it prints ALL kernel messages right after boot, i'm using -c option in order to remove logs. However, kernel messages can come out anytime even when i don't even want it. So there might be a interrupt even if i use dmesg | grep command, after iwpriv [interface] show [parameter] command.,

So, are there anyways to save kernel message for a specific commands?