Guard + Pry + Mac OS X = :-(

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Debugging is critical, especially when you’re learning a new system. At Ibotta, we’re using pry for debugging. Today, I ran into an issue where I had Guard running to automatically run my tests as I made changes. I need a breakpoint, so I set a binding.pry in a model I wanted to inspect. Upon hitting the breakpoint, I noticed that what I was typing was not being echoed to the screen. I could still execute commands, but I couldn’t see what I was typing. Pretty annoying!

How to Fix It

The reason behind this problem turns out to be the version of Ruby I built using rbenv and ruby-build. It uses the libedit instead of readline. There are a few ways to fix this problem detailed on Guard’s wiki.

The Easy Way

The easy way for me turned out to be adding rb-readline to my Gemfile, like this:

group :development do
  gem 'rb-readline'

The Harder Way

But, of course, I did it the hard way first. I rebuild Ruby with the readline version I had installed on my Mac.

First, install readline:

brew install readline

Then, reinstall the version of Ruby you’re using:

RUBY_CONFIGURE_OPTS=--with-readline-dir=`brew --prefix readline` rbenv install 1.9.3-p286


All of these options are actually defined on the Guard Wiki, so check that out if you’re still having problems.

Find an issue?
Open a pull request against my blog on GitHub.
Ben Limmer