Rails quick tips #7: Project-specific .irbrc

In a previous installment of this series, I wrote about adding a project-specific .pryrc to Ruby/Rails projects. However, over the past couple of years, IRB gained some nice features and I don’t use Pry much anymore because it’s one less dependency I need to worry about. That doesn’t mean I want to give up on per-project configuration files though, which turned out to be slightly more complicated with IRB.

#Configuration file lookup

The way IRB and Pry load their configuration is significantly different. Pry looks for $XDG_CONFIG_HOME/pry/pryrc or ~/.pryrc first and then loads the .pryrc file in the current directory if it exists (source). IRB will look for other configuration files only if ~/.irbrc doesn’t exist and it will do so in the following order (source):

IRB reads from ~/.irbrc when it’s invoked.

If ~/.irbrc doesn’t exist, irb will try to read in the following order:

• .irbrc
• irb.rc
• _irbrc
• $irbrc

This is a bit of a problem since I often work on more than one Ruby/Rails project and want to keep my general configuration in ~/.irbrc while being able to override/augment it with an additional local file.

#The solution

This is what I came up with to solve this problem.

1. Add the IRBRC environment variable to the project’s .envrc. I pretty much always use direnv, so this works well for me.

   export IRBRC="./.irbrc.local"
   

2. Load the global .irbrc from the local file and add whatever else I need:

   load File.expand_path("~/.irbrc")
   
   # just an example
   def user
     @user ||= User.first
   end
   

3. Add .irbrc.local and .irbrc.local_history to either .gitignore or ~/.gitignore (I did the latter).

While I do prefer Pry’s approach overall, this is easy enough to set up and configure.