tty

• Print the file name of the terminal connected to standard input.

tty

• The output is /dev/ttyN, when a "root" tty
• Where N is the number of the tty, as switched by Ctrl + Alt + Fn
• The output is /dev/pts/N, when a "virtual" tty
• When running from a terminal emulator, for instance

Autostart a DE when logging in

# .bash_profile (bash)
# .zlogin or .zprofile (Zsh)
[ "$(tty)" = "/dev/tty1" ] && exec sway