Add Run Commands With Specific Rails Version as a Rails TIL

Author: jbranchaud

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).
 
-_1368 TILs and counting..._
+_1369 TILs and counting..._
 
 ---
 
@@ -899,6 +899,7 @@ _1368 TILs and counting..._
 - [Rollback A Specific Migration Out Of Order](rails/rollback-a-specific-migration-out-of-order.md)
 - [Rounding Numbers With Precision](rails/rounding-numbers-with-precision.md)
 - [Run A Rake Task Programmatically](rails/run-a-rake-task-programmatically.md)
+- [Run Commands With Specific Rails Version](rails/run-commands-with-specific-rails-version.md)
 - [Run Some Code Whenever Rails Console Starts](rails/run-some-code-whenever-rails-console-starts.md)
 - [Schedule Sidekiq Jobs Out Into The Future](rails/schedule-sidekiq-jobs-out-into-the-future.md)
 - [Secure Passwords With Rails And Bcrypt](rails/secure-passwords-with-rails-and-bcrypt.md)

rails/run-commands-with-specific-rails-version.md

@@ -0,0 +1,30 @@
+# Run Commands With Specific Rails Version
+
+You can have multiple versions of a gem like `rails` installed with `gem`.
+However, when you go to run a rails command, your system will default to using
+the latest version that you have installed.
+
+So doing a version check will show that version to currently be `7.1.3` and
+running something like `rails new` will set up a new Rails 7.1.3 app.
+
+```bash
+$ rails --version
+Rails 7.1.3
+
+$ rails new my_app
+```
+
+If you want to use a Rails version besides the latest you have installed for
+whatever command, you can use a `gem` convention which is to put `_<VERSION>_`
+right after the gem name.
+
+Let's try this for Rails 6.1.3:
+
+```bash
+$ rails _6.1.3_ --version
+Rails 6.1.3
+
+$ rails _6.1.3_ new my_app
+```
+
+[source](https://stackoverflow.com/a/452458/535590)