expect_background affecting other expect's behavior - expect

Question

I'm writting an expect script to automate some tests. To detect when a general error occurs (which can happen at any phase of the test), instead of repeating the same pattern (for instance, "Rebooting system") on each expect command, I decided to use expect_background for that kind of condition.
What I understand about the expect_background command is that it is checked against all input text before the currently active expect. So, if both expect_background and expect are waiting for the same pattern, I expect (with the pun, please ;-) ) both actions to be triggered. For instance:
#!/usr/bin/expect -f
spawn ./counter.sh
expect_background {
"5" { puts "expect-bg"; }
}
expect {
"9" { puts "expect-9"; }
}
expect {
"20" { puts "expect-20"; }
}
The ./counter.sh script counts from 1 to 20 with intervals of 1 second. According to the behavior I described above, "expect-bg" should be printed at 5 and 15, expect-9 at 9, and "expect-20" at 20. But here is what I get:
$ ./expect_bg.expect
spawn ./counter.sh
1
2
3
4
5
expect-bg
6
7
8
9
10
11
12
13
14
15
expect-bg
16
17
18
19
20
Why is that happening? And how to I get the behavior described?

Answer 1

I can produce your desired output with expect_before and exp_continue
#!/usr/bin/expect -f
spawn sh counter.sh
expect_before {
5 {puts "expect_before"; exp_continue}
}
expect {
9 {puts "exp_9"}
}
expect {
20 {puts "exp_20"}
}
$ expect counter.exp
spawn sh counter.sh
1
2
3
4
5
expect_before
6
7
8
9
exp_9
10
11
12
13
14
15
expect_before
16
17
18
19
20
exp_20
When you have
expect_before {
5 {puts "expect_before"; exp_continue}
}
expect {
9 {puts "exp_9"}
}
you effectively have this:
expect {
5 {puts "expect_before"; exp_continue}
9 {puts "exp_9"}
}
If you omit the exp_continue, that expect statement ends with the first 5, so you never get a chance to look for 9.