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.

You will need to `expect` another pattern to be able to break out of the loop. Otherwise you'll never get to the `interact` line. — glenn jackman, Jul 13 '13 at 11:47

score 24 · Answer 1 · edited Nov 02 '18 at 17:12

24

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"
    }
}

edited Nov 02 '18 at 17:12

Anthony Geoghegan

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answered Oct 19 '18 at 13:55

jbtule

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2

I've already upvoted the accepted answer but this one is much more elegant (Don't Repeat Yourself); `exp_continue` works well to solve the optional prompt problem. – Anthony Geoghegan Nov 02 '18 at 17:15
This one is neat. – jdhao Oct 12 '19 at 03:13

score 18 · Accepted Answer · answered Jul 12 '13 at 19:35

18

You can expect multiple things:

expect { 
    "prompt2" { 
        send "pass2"
        expect "prompt3"
        send "pass3"
    }
    "prompt3" {
        send "pass3"
    }
}

answered Jul 12 '13 at 19:35

that other guy

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Oh man, didn't see this but this is near identical to my fix. – joshualan Jul 12 '13 at 19:40
6

How would one avoid the `prompt3`/`pass3` code duplication? – Abdull Mar 04 '16 at 11:00

How to use expect with optional prompts?

2 Answers2

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