How to get the sub-process pid in the expect shell script, after spawn

Question

Part of the script a.exp:

#!/usr/bin/expect
# ..... 
spawn ssh -qTfnN -D $port $user@$host
expect "*assword:*"
# .....

How can I get the pid of sub-process "ssh".

If I execute these in bash shell, not in a script file, the result is

expect1.1> spawn ssh name@host
spawn ssh name@host
2188
expect1.2> 

2188 is the sub-process pid.

And how to use exp_pid command in the expect shell?

Answer 1

I think that what you're looking for is something like this:

spawn ssh name@host
set pid [exp_pid]
puts "PID: $pid"

Answer 2

This man page says:

spawn returns the UNIX process id. If no process is spawned, 0 is returned.

I.e. you can do:

set pid [spawn ssh -qTfnN -D $port $user@$host]

---

You can also use exp_pid as jcollado demonstrated. The same man page explains that:

exp_pid [-i spawn_id]
returns the process id corresponding to the currently spawned process. If the -i flag is used, the pid returned corresponds to that of the given spawn id.