определение подключён ли клиент по ssh

env | grep SSH_

u@srv0:~> w
20:01  up 14 mins, 1 user, load averages: 0,00 0,02 0,05
USER       TTY      FROM                      LOGIN@  IDLE WHAT
u          pts/0    10.10.10.11              20:01       - w

[21:23][leave][~]$ w
 21:23:32 up 11 days, 31 min,  4 users,  load average: 1.06, 0.94, 1.04
USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU WHAT
leave    pts/0    :0.0             15Sep12  9:17m  0.23s  0.05s /bin/bash
leave    pts/1    :0.0             Sat15    0.00s  1.70s  1.69s /bin/bash
leave    pts/2    :0.0             15Sep12 11days  0.00s  1:03  kdeinit4: kded4 [kdeinit]       
leave    pts/4    :0.0             Sat15    2days  1.06s  1.06s /bin/bash

[21:23][leave][~]$ ssh localhost -p 2200
leave@localhost's password: 

[21:23][leave][~]$ w
 21:23:39 up 11 days, 31 min,  5 users,  load average: 1.06, 0.94, 1.04
USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU WHAT
leave    pts/0    :0.0             15Sep12  9:17m  0.23s  0.05s /bin/bash
leave    pts/1    :0.0             Sat15    0.00s  1.73s  1.70s /bin/bash
leave    pts/2    :0.0             15Sep12 11days  0.00s  1:03  kdeinit4: kded4 [kdeinit]       
leave    pts/3    localhost        21:23    0.00s  0.06s  0.00s w
leave    pts/4    :0.0             Sat15    2days  1.06s  1.06s /bin/bash

if [[ -z "$SSH_CLIENT" ]]; then
        prompt="123"
else
        prompt="234"
fi