$ write username tty

$ w
USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU WHAT
user     :0       :0               08:15   ?xdm?   7:37   0.25s init --user
user     pts/0    :0               08:19    1.00s  0.09s  0.01s w
user     pts/12   :0               08:50   54.00s  0.03s  0.03s bash

$ ls | write username pts/12

ls > /dev/pts/7

ls > /proc/5555/fd/0