expect script if password else user/password - if-statement

Question

My situation is that i have to bacup the config of some switches.
The authentication on switches is by password and user/password
I cannot seem to find an expect script that checks to login first with just password, and if it fails then to try user and password.
it should be something like:
telnet to host
if password ok then execupt backup command
else send user and password and execute backup command
#!/usr/bin/expect
spawn telnet 172.21.146.22
sleep 1
send "\x19"
sleep 1
expect
{
"Password:" {
send "pass\r"
interact
}
"Username:" {
send "admin\r"
sleep 1
expect "Password:"
send "pass\r"
interact
}
}

Answer 1

What you need here is exp_continue, that basically enables "looping" in an expect statement
#!/usr/bin/expect
spawn telnet 172.21.146.22
sleep 1
send "\x19"
sleep 1
expect { # <-- open braces *must* be on same line as command.
"Password:" {
send "pass\r"
exp_continue
}
"Username:" {
send "admin\r"
exp_continue
}
timeout {
error "timed out before successful login"
}
"some_string_you_see_when_you_have_logged_in_successfully"
}
send "your backup command\r"
If, when you login, you see the Password prompt first, you'll send that password but stay inside the expect command until some other pattern is seen. If that is "Username", then you'll send the username and then wait until the password prompt is seen. If the first password succeeded then you'll need to look for "some_string_you_see_when_you_have_logged_in_successfully"