From 93398ab9507dfaab31d76153b4036edbb0356358 Mon Sep 17 00:00:00 2001
From: jbranchaud <jbranchaud@gmail.com>
Date: Thu, 13 Mar 2025 10:31:32 -0500
Subject: [PATCH] Add Add Color To The IRB Console Prompt as a Rails TIL

---
 README.md                                    |  3 +-
 rails/add-color-to-the-irb-console-prompt.md | 62 ++++++++++++++++++++
 2 files changed, 64 insertions(+), 1 deletion(-)
 create mode 100644 rails/add-color-to-the-irb-console-prompt.md

diff --git a/README.md b/README.md
index c87d782..6d11812 100644
--- a/README.md
+++ b/README.md
@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1616 TILs and counting..._
+_1617 TILs and counting..._
 
 See some of the other learning resources I work on:
 - [Ruby Operator Lookup](https://www.visualmode.dev/ruby-operators)
@@ -977,6 +977,7 @@ If you've learned something here, support my efforts writing daily TILs by
 - [Add A Generated Column To A PostgreSQL Table](rails/add-a-generated-column-to-a-postgresql-table.md)
 - [Add A Reference Column With An Index](rails/add-a-reference-column-with-an-index.md)
 - [Add ActiveRecord Error Not Tied To Any Attribute](rails/add-activerecord-error-not-tied-to-any-attribute.md)
+- [Add Color To The IRB Console Prompt](rails/add-color-to-the-irb-console-prompt.md)
 - [Add React With Webpacker To A New Rails App](rails/add-react-with-webpacker-to-a-new-rails-app.md)
 - [Add timestamptz Columns With The Migration DSL](rails/add-timestamptz-columns-with-the-migration-dsl.md)
 - [Adjust The Production Log Level](rails/adjust-the-production-log-level.md)
diff --git a/rails/add-color-to-the-irb-console-prompt.md b/rails/add-color-to-the-irb-console-prompt.md
new file mode 100644
index 0000000..ff7fb13
--- /dev/null
+++ b/rails/add-color-to-the-irb-console-prompt.md
@@ -0,0 +1,62 @@
+# Add Color To The IRB Console Prompt
+
+IRB has a little-known [`Color`
+module](https://docs.ruby-lang.org/en/3.2/IRB/Color.html) with some helpers for
+adding a splash of color to the IRB prompt. I like to clearly differentiate the
+environment I'm in when connecting to the `rails console`, so I have a
+customize the prompt to display and colorize the current environment.
+
+I can wrap any string in ANSI escape codes that instruct the terminal to style
+the text with color. For instance, here is how I can style the word `DEV` to be
+inverted against a blue background.
+
+```ruby
+IRB::Color.colorize("DEV", [:BLUE, :BOLD, :REVERSE])
+```
+
+which will clearly stand out from `PROD` against a red background:
+
+```ruby
+IRB::Color.colorize("PROD", [:RED, :BOLD, :REVERSE])
+```
+
+Here is a full example of customizing the prompt from the
+`config/application.rb` file.
+
+```ruby
+module MyApp 
+  class Application < Rails::Application
+    # ...
+
+    console do
+      # Get the application module name and convert to kebab-case
+      app_name = Rails.application.class.module_parent.name
+      kebab_name = app_name.underscore.dasherize
+
+      # Environment color coding
+      env_colors = {
+        "development" => IRB::Color.colorize("DEV", [:BLUE, :BOLD, :REVERSE]),
+        "production" => IRB::Color.colorize("PROD", [:RED, :BOLD, :REVERSE]),
+        "test" => IRB::Color.colorize("TEST", [:YELLOW, :BOLD, :REVERSE]),
+      }
+
+      colored_env = "(#{env_colors[Rails.env]})"
+
+      # Docs: https://docs.ruby-lang.org/en/3.2/IRB.html#module-IRB-label-Customizing+the+IRB+Prompt
+      IRB.conf[:PROMPT][:RAILS_APP] = {
+        PROMPT_I: "#{kebab_name}#{colored_env}> ",
+        PROMPT_N: "#{kebab_name}#{colored_env}* ",
+        PROMPT_S: "#{kebab_name}#{colored_env}% ",
+        PROMPT_C: "#{kebab_name}#{colored_env}? ",
+        RETURN: "=> %s\n"
+      }
+
+      # Set it as the current prompt
+      IRB.conf[:PROMPT_MODE] = :RAILS_APP
+    end
+  end
+end
+```
+
+The Ruby docs have more about [IRB Prompt
+Customization](https://docs.ruby-lang.org/en/3.2/IRB.html#module-IRB-label-Customizing+the+IRB+Prompt).