Well, the automatic public key installation is what I want to achieve on the LAN, so I've tried to call ssh-copy-id to the remote pc, which asks for the password and doesn't have an option to pass password by cli.
I am considering to reimplement the needed ssh-copy-id's functionality in perl, by using Net::SSH2 module, but before that, I wonder, if there is a way to, instead of using /dev/tty trick, emulate the keyboard to send the keys to the program. Make a perl program to act as if the keyboard would send the keys to the program, like you can do in the GUI programming, to send keyboard keystrokes.