Expect script connects with ssh but does not run commands

Question

I need to write a script that runs on a PC with Centos 7 and connects to another PC with Centos 7 using ssh, execute a console command, for example "ls -la" and save the output of it to a file to be able to later analyze that output.

I have written the following EXPECT script:

ssh_connection.exp :

#!/usr/bin/expect -f
set timeout 120
spawn ssh [email protected]
expect "assword:"
send "PASSWORD\r"
expect "prompt#"
sleep 5
puts "Executing ls -la"
send "ls -la\r"
sleep 10
puts "Executing ps -af"
puts "ps -af\r"
sleep 10
puts "Closing the ssh session\r"
send "exit\r"

This script connects correctly through ssh to the machine with IP = 129.0.0.10 and displays on the screen the messages that appears on "puts": Executing ls -la Executing ps -af Closing the ssh session

However, it does not show the result of executing the commands I send with send:

ls -la
ps -af

What is wrong with this script?

How can I make the output of the previous commands saved in a file to be able to analyze it later with a bash script or a C program?

Answer 1

You don't need to use expect to do this. The ssh command can take additional arguments of commands you want to run via the SSH connection.

Step #1

Setup a SSH key pair (google it) and then copy the SSH key to the remote server. To do this I'd recommend using ssh-copy-id. See my answer to this U&L Q&A titled: How to properly copy private keys from remote servers to my localmachine so I can connect using ssh.

Step #2

Now with the ability to SSH to a server in place using a key, your above problem turns into this:

$ ssh [email protected] "ls -la; ps -af"

You can get fancy and use here documents (heredocs aka. here-docs) to further enhance this technique.

$ ssh [email protected] <<EOF
> ls -la
> ps -af
> EOF

or put the commands in a file and pass them to ssh:

$ ssh [email protected] < my.cmds

Answer 2

Thanks,

I have modified my script replacing the line:

spawn ssh [email protected]

with this other, as you tell me:

spawn ssh [email protected] "ls -la; ps -af"

Now I see the commands output on the screen and I can redirect to a file.

Next I tried to adapt this script to execute a command on another machine that is a Cisco like switch (it is not Cisco, but it is compatible).

The script with which I connect to the switch using ssh is:

**#!/usr/bin/expect -f

set timeout 120

spawn ssh [email protected] "show vlan 500"

expect "assword:"

send "PASSWORD\r"

expect "prompt#"

sleep 5

puts "Closing the ssh session\r"

send "exit\r"**

>

This does not work on the switch and I get this error:

spawn ssh [email protected] show vlan 501

[email protected]'s password:

imish: invalid option -- 'c'

Try `imish --help' for more information.

send: spawn id exp6 not open

while executing

"send "exit\r""

(file "./ssh_script_v3.exp" line 7)

>

So I must use the expect script that send the command using "send" :

!/usr/bin/expect

spawn ssh [email protected]

expect "assword:"

send "user\r"

expect ">"

sleep 5

send "sh vlan 500\r"

sleep 5

send "exit\r"

>

Now I do not get any error, but nothing is shwon on the screen.

I have read that this happens because linux and UNIX systems automatically buffer their output when running non-interactively. I think that Expect can make the programs think they are running interactively by means of "unbuffer", but I do not know how to use "unbuffer" with "send". My attemps to do this, do not work.