How to use expect with optional prompts?

Question

Let's say I am trying to write an expect script for a test.sh that has three prompts: prompt1, prompt2, prompt3.

My code is like this:

spawn test.sh
expect "prompt1"
send "pass1"
expect "prompt2"
send "pass2"
expect "prompt3"
send "pass3"

However, prompt2 only occurs half the time. If prompt2 doesn't show up, the expect script breaks. How would I write expect code that skips over prompt2 if it doesn't show up?

EDIT:

Fixed my code:

/usr/bin/expect -c '
spawn ./test.sh
expect {
      "prompt1" {
          send "pass1\r"
          exp_continue
      }
      "prompt2" {
          send "pass2\r"
          exp_continue
      }
      "prompt3" {
          send "pass3\r"
          exp_continue
      }
}
interact return
'

This way, the rest of the script executes and provides output.

Answer 1

As long as you have a case that will be always be expected to hit and don't include an exp_continue in that case, you can can remove duplication and handle optional prompts easily:

expect "prompt1"
send "pass1"
expect { 
    "prompt2" { 
        send "pass2"
        exp_continue
    }
    "prompt3" {
        send "pass3"
    }
}