#MOO, 81/75/41/35 bytes

while(!player:tell(read(player)))endwhile

or, 36 byte version if being run with wizard permissions:

while(!player:tell(read()))endwhile

Each of these versions will wait for a newline before printing, unless set_connection_option(player, "binary", 1) (40 bytes long) is called previously, as that is the nature of the input system.

MOO, 81/75/41/35 bytes

while(!player:tell(read(player)))endwhile

or, 36 byte version if being run with wizard permissions:

while(!player:tell(read()))endwhile

Each of these versions will wait for a newline before printing, unless set_connection_option(player, "binary", 1) (40 bytes long) is called previously, as that is the nature of the input system.