Spawning an interactive telnet session from a shell script
Question
I'm trying to write a script to allow me to log in to a console servers 48 ports so that I can quickly determine what devices are connected to each serial line.
Essentially I want to be able to have a script that, given a list of hosts/ports, telnets to the first device in the list and leaves me in interactive mode so that I can log in and confirm the device, then when I close the telnet session, connects to the next session in the list.
The problem I'm facing is that if I start a telnet session from within an executable bash script, the session terminates immediately, rather than waiting for input.
For example, given the following code:
$ cat ./telnetTest.sh
#!/bin/bash
while read line
do
telnet $line
done
$
When I run the command 'echo "hostname" | testscript.sh' I receive the following output:
$ echo "testhost" | ./telnetTest.sh
Trying 192.168.1.1...
Connected to testhost (192.168.1.1).
Escape character is '^]'.
Connection closed by foreign host.
$
Does anyone know of a way to stop the telnet session being closed automatically?
Solution
You need to redirect the Terminal input to the telnet
process. This should be /dev/tty
. So your script will look something like:
#!/bin/bash
for HOST in `cat`
do
echo Connecting to $HOST...
telnet $HOST </dev/tty
done
OTHER TIPS
I think you should look at expect program. It`s present in all modern linux distros. Here is some exmaple script:
#!/usr/bin/expect -f
spawn telnet $host_name
expect {
"T0>" {}
-re "Connection refused|No route to host|Invalid argument|lookup failure"
{send_user "\r******* connection error, bye.\n";exit}
default {send_user "\r******* connection error (telnet timeout),
bye.\n";exit}
}
send "command\n"
expect -timeout 1 "something"
spawn command start remote login program (telnet, ssh, netcat etc)
expext command used to... hm.. expect something from remote session
send - sending commands
send_user - to print comments to stdout
Thanks Dave - it was the TTY redirection that I was missing.
The complete solution I used, for those who are interested:
#!/bin/bash
TTY=`tty` # Find out what tty we have been invoked from.
for i in `cat hostnames.csv` # List of hosts/ports
do
# Separate port/host into separate variables
host=`echo $i | awk -F, '{ print $1 }'`
port=`echo $i | awk -F, '{ print $2 }'`
telnet $host $port < $TTY # Connect to the current device
done
Telnet to Server using Shell Script Example:
Test3.sh
File:
#!/bin/sh
#SSG_details is file from which script will read ip adress and uname/password
#to telnet.
SSG_detail=/opt/Telnet/SSG_detail.txt
cat $SSG_detail | while read ssg_det ; do
ssg_ip=`echo $ssg_det|awk '{print $1}'`
ssg_user=`echo $ssg_det|awk '{print $2}'`
ssg_pwd=`echo $ssg_det|awk '{print $3}'`
echo " IP to telnet:" $ssg_ip
echo " ssg_user:" $ssg_user
echo " ssg_pwd:" $ssg_pwd
sh /opt/Telnet/Call_Telenet.sh $ssg_ip $ssg_user $ssg_pwd
done
exit 0
The Call_Telenet.sh
script is as follows:
#!/bin/sh
DELAY=1
COMM1='config t' #/* 1st commands to be run*/
COMM2='show run'
COMM3=''
COMM4=''
COMM5='exit'
COMM6='wr'
COMM7='ssg service-cache refresh all'
COMM8='exit' #/* 8th command to be run */
telnet $1 >> $logfile 2>> $logfile |&
sleep $DELAY
echo -p $2 >> $logfile 2>> $logfile
sleep $DELAY
echo -p $3 >> $logfile 2>> $logfile
sleep $DELAY
echo -p $4 >> $logfile 2>> $logfile
sleep $DELAY
echo -p $5 >> $logfile 2>> $logfile
sleep $DELAY
sleep $DELAY
sleep $DELAY
sleep $DELAY
echo -p $COMM7 >> $logfile 2>> $logfile
sleep $DELAY
echo -p $COMM8 >> $logfile 2>> $logfile
sleep $DELAY
exit 0
Run the above file as follows:
$> ./test3.sh
Perhaps you could try bash -i to force the session to be in interactive mode.
The problem in your example is that you link the input of your script (and indirectly of telnet
) to the output of the echo
. So after echo
is done and telnet
is started, there is no more input to read. A simple fix could be to replace echo "testhost"
by { echo "testhost"; cat; }
.
Edit: telnet
doesn't seem to like taking input from a pipe. However, netcat
does and is probably just suitable in this case.
@muz I have a setting with ssh, no telnet, so i can't test if your problem is telnet related, but running the following script logs me successively to the different machines asking for a password.
for i in adele betty
do
ssh all@$i
done
If your environment is X11-based, a possibility is to open an xterm running telnet:
xterm -e telnet $host $port
Operations in xterm are interactive and shell script is halted until xterm termination.
Try these links.
http://planetozh.com/blog/2004/02/telnet-script/
http://www.unix.com/unix-dummies-questions-answers/193-telnet-script.html
#!/bin/sh
( echo open hostname
sleep 5
echo username
sleep 1
echo password
sleep 1
echo some more output, etc. ) | telnet
They worked for me :D