How to send output from one terminal to another without making any new pipe or file

If both terminals belong to the same user, you can send your output to the virtual device that is used as the particular terminal's tty.

So you can use the output from w, which includes the TTY information, and write directly to that device.

ls > /dev/pts/7

(If the device mentioned by w was pts/7)

Another option is to use the number of a process that is connected to that device. Send your output to /proc/<process number>/fd/1.

ls > /proc/5555/fd/1

Assuming the process number that you found that runs in that terminal is 5555.

Note that this direct write is only allowed if the user that attempts to write is the same user that owns the other terminal.

You can use write command.

As @MelBurslan commented, if write permission is off, first execute:

 $ mesg y

From man mesg

OPTIONS

y Allow write access to your terminal.

Usage of write:

$ write username tty

e.g. Send ls output to other terminal.

$ 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

I found a similar method.

On first terminal:

 $ tty
 /dev/pts/0
 $ <no need to run any command here, just see the output>

On second terminal:

$ ls > /dev/pts/0

Now you get the output on first terminal