Since bitcoin core is HD wallet, it should be possible to make "seed" like backup for it and there should be way to restore the wallet from it as well. I know there is dumpprivkey, but it needs to be done after every transaction to be safe. Other wallets have nice seed backup and restore methods, I suppose core should have one as well.
There is xprv method mentioned in comments, but I'm still missing restore method. Also I would like to do it from console only, since my wallet is on remote server without graphics.
I'm interested in "string" backup mainly because I want to store it in trezor hardware password manager, which does not support files