I recently re-ran some Ansible provisioning scripts after upgrading the base box to an Ubuntu 14.04 image and found they stalled midway through. The cause? One task involved installing the PECL mongo module, and the installation process now prompts the user to decide whether or not to build with Cyrus SASL support. I couldn’t see a way to force a decision via the PECL installer, and Ansible can’t respond to the prompt, so the provisioning process hung while awaiting an answer.

I found two ways to solve this.

I’ve been expecting you

I did a bit of Googling and after coming across this post on the Ansible forum, I took a look at expect. Expect lets you script interactions with a spawned command, using regex to match against prompt text, and send appropriate responses. It’s a sound approach; I wrote a script that looked like this:

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#!/usr/bin/expect

spawn pecl install mongo

expect "Build with Cyrus SASL"
send "\r"

expect eof

And executed it on the box using Ansible’s script module:

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- name: Install PECL mongo extension
  script: install_pecl_mongo.expect

Mission achieved. I felt very pleased with myself for about 30 seconds, which is how long it took for Paul to wander over and tell me there was a simpler way to do it. Expect is a really good solution for scripting varied or complex responses, but I wasn’t faced with that problem here…

Yes man

In this specific case, all I wanted to do was answer a prompt which needed a yes or no answer, and I wasn’t concerned which I went with. There’s a linux command called yes which “outputs an affirmative response, or a user-defined string of text continuously until killed”, which is just what I needed.

So now my task looks like this:

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- name: Install PECL mongo extension
  shell: yes '' | pecl install mongo

Which continuously pipes the ‘y’ character (by default) and a newline character into the install command, automatically causing any prompts to be responded to in the affirmative. For my simple use case it works perfectly, and is more straightforward than writing expect scripts.