Using a tcl proc to login to devices - tcl

Question

I have a tcl (expect) script to log into devices and transfer files. Unfortunately, the files are large, and during the transfer period the ssh connection ends (the files are still transferred though). So I basically have to login again before I can perform more actions on the device. Since the whole login process is long, I put it in a proc. The issue is that the proc logs into the device, but after the login, the script sends the commands to the terminal as, for some reason, the commands no longer reach the device. I cant figure out why the session I logged into in the proc does not carry over to the rest of the script.
proc login {} {
#login code - it works because I took it from the main script (which works).
# variables are all declared as global, no errors are thrown. Login is successful
}
login
send "show\r" ;# this command is not sent to the device,
#instead it prints to the terminal. When in the main script,
#these commands would not be printed to the terminal window.
Is there a command I am missing to maybe return the login session to the rest of the script? something similar to the interact command, but to the rest of the script.

Answer 1

This is a tricky one. The expect man page says this:
Expect takes a rather liberal view of scoping. In particular, variables read by commands specific
to the Expect program will be sought first from the local scope, and if not found, in the global
scope. For example, this obviates the need to place "global timeout" in every procedure you write
that uses expect. On the other hand, variables written are always in the local scope (unless a
"global" command has been issued). The most common problem this causes is when spawn is executed in
a procedure. Outside the procedure, spawn_id no longer exists, so the spawned process is no longer
accessible simply because of scoping. Add a global spawn_id to such a procedure.
So, add global spawn_id as the first line of the login proc

Answer 2

To make a procedure that evaluates code in its caller's scope, you need to use the uplevel command inside it. This lets you do what is essentially a macro very easily:
proc login {} {
uplevel {
# Put your code in here, which might look like this
spawn ssh user#host ...
expect Password:
send $thePassword\r
expect "bash$"
}
}
Then, when you use login it will work exactly like the commands you have inside the uplevel in the procedure, as if they'd been typed in place of the login call.
This isn't usually a particularly recommended approach, as it is very easy to make code that is inflexible and inclined to break unexpectedly, but in your case it is a very easy approach since you can easily guarantee to only call login at a sensible place in the overall program structure. (The uplevel command is more commonly used with scripts passed in with arguments — it's just like you're passing in a block — but that's not what you need.)