How does Expect script determine contents of expect_out - bash

Question

I am trying to write a script will provide credentials to a vpn with one caveat where VPN requires that I provide OTP.
This is my script:
#! /usr/bin/expect
set vpn [ lindex $argv 0]
set group [ lindex $argv 1]
set user [ lindex $argv 2]
set secret [ lindex $argv 3]
log_user 2
spawn nmcli con up $vpn --ask
expect {
"GROUP:" {
send "$group\r"
exp_continue
}
"Username:" {
send "$user\r"
exp_continue
}
Password: {
send_user "\nProvide RSA OTP:"
expect_user -re ":(.*)\r"
set otp $expect_out(0,string) <--------- Error!!!
set pass "$secret$otp"
send "$pass\r"
exp_continue
}
"Connection successfully activated" {
send_user "Connected to VPN\r"
}
"Login failed" {
send_user "Login failed\r"
exp_continue
}
"already active" {
send_user "Already connected to VPN\r"
}
}
exit
I included an arrow to what I think is the source of the problem because when I run this script, it looks like expect_out contains Password:. Given what i read in man page I imagined that the buffer is cleared each time new match is made and therefore it contains string matched in most recent expect clause( in this case expect_user -re ":(.*)\r"), however it seems that I'm wrong. I did not see any notes saying that expect_user contents need to be accessed using different function like interact does, so I'm not sure where did my password go?
Thank you

Answer 1

When using send_user you will not see an echo of what you write, unlike when you send to the spawned command, so you will never match : unless the user explicitly types it. Also, you will read newline, not carriage-return. So use
expect_user -re "(.*)\n"
to get the user input and $expect_out(1,string) (1 not 0) will contain the input.
What you are observing is a timeout in your expect_user, which is why the variable is not updated and still contains the old match.
To protect yourself against unseen timeouts, you could set up a "global" timeout check by starting with
proc abort { } { send_user "Timeout!" ; exit 2 }
expect_before timeout abort
The expect_before is done "before" each expect, but also before each expect_user, it seems.