Read program output from stdin instead of using spawn - shell

Question

I'm trying to write a shell function that spawns a ssh process and authentificates with a password. Then, I'd like to use the spawned process to do further stuff with expect.
Here's the function I have so far:
ssh_cmd() {
ssh $USER#$HOST 2>&1 | expect -c "
log_user 0
set timeout 5
expect password: {
send \"$PASS\n\"
sleep 2
log_user 1
}
"
}
And then I'd like to use given function in other places to interact with the ssh process like this:
ssh_cmd | expect -c "
expect '#' {
send pwd\n
send exit\n
}
expect eof
"
However, running the ssh_cmd function with -d option for expect I get the following result:
expect version 5.45.4
expect: does "" (spawn_id exp0) match glob pattern "password:"? no
ubnt#ui1's password: expect: timed out
From what I understand, the output of ssh does not get piped correctly. I know the common way to do this would be to use spawn, but that would mean the process would get killed after expect exits and I could not have a generic function that authentificates ssh sessions and keeps the process alive for further usage.

Answer 1

What you're designing won't work. Expect needs the process to be spawned from within the expect interpreter using the spawn command. Passing the command's stdout into expect is insufficient.
You could try this:
ssh_cmd() {
# a default bit of code if user does not provide one.
# you probably want some checking and emit an error message.
local user_code=${1:-set timeout 1; send "exit\r"; expect eof}
expect -c "
log_user 0
set timeout 5
spawn ssh -l $USER $HOST
expect password: {
send \"$PASS\n\"
sleep 2
log_user 1
}
$user_code
"
}
and then invoke it like:
ssh_cmd '
expect "#" {
send pwd\r
send exit\r
}
expect eof
'
Note that single quotes have no special meaning in expect, they are just plain characters: you probably don't want to expect the prompt to be the 3 character pattern '#'