Find currently connected port number SSH

Question

i'm creating a local simulator (not connected to internet) using SSH connection. I've started sshd on a particular range of port numbers and NATing a range of devices to those. I have to find the currently connected port number.

OS CentOS 5.5 OpenSSH 6.1

I've done the following. It works for normal usage (manual user).But when trying a rigorous testing(automated) it seems like it is failing sometimes to find the port number.

#!/bin/bash

WHOINFO=`who -m`

USERNAME=`echo $WHOINFO | awk 'NR==1{print $1}'`
PTSNUMBER=`echo $WHOINFO | awk 'NR==1{print $2}'`

USERSTR=$USERNAME"@"$PTSNUMBER

PID=`ps -eLf | grep $USERSTR | awk 'NR==1{print $3}'`

if [ -z "$PID" ];
then
        exit
fi

PORTSTR=`netstat -natp | grep $PID | awk 'NR==1{print $4}'`

PORTNUMBER=${PORTSTR//*:/}

echo $PORTNUMBER

Solution

An OpenSSH server will set the variable $SSH_CLIENT, which contains the current ip, client port and server port separated by spaces:

$ echo "$SSH_CLIENT"
127.0.0.1 59064 22

To get the port number the current session is connected to, you can therefore use echo ${SSH_CLIENT##* }.

Comments

[Anya Shenanigans]

and if he wants to he can read that environment variable from the /proc/<pid>/environ file by piping it through tr '\0' '\n'

[Antarus]

@that other guy Brilliant! my entire script now got reduced to an echo command. I couldn't find this variable. Thnx.