Add List All Installable Rails Versions as a Rails til

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://tinyletter.com/jbranchaud).
 
-_992 TILs and counting..._
+_993 TILs and counting..._
 
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@@ -625,6 +625,7 @@ _992 TILs and counting..._
 - [Hash Slicing](rails/hash-slicing.md)
 - [Ignore Poltergeist JavaScript Errors](rails/ignore-poltergeist-javascript-errors.md)
 - [Inspect Previous Changes To ActiveRecord Object](rails/inspect-previous-changes-to-activerecord-object.md)
+- [List All Installable Rails Versions](rails/list-all-installable-rails-versions.md)
 - [List The Enqueued Jobs](rails/list-the-enqueued-jobs.md)
 - [Log SQL Queries Executed By ActiveRecord](rails/log-sql-queries-executed-by-activerecord.md)
 - [Mark A Migration As Irreversible](rails/mark-a-migration-as-irreversible.md)

rails/list-all-installable-rails-versions.md

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+# List All Installable Rails Versions
+
+_Here's a [screencast](https://www.youtube.com/watch?v=IizkvqGLkhU) in case you
+want to watch instead of read._
+
+I [was curious](https://twitter.com/jbrancha/status/1345467867479875584?s=20)
+what versions of Rails were remotely available to be installed with `gem`. On
+its own, `gem list rails` will show all _locally_ installed gems that
+partially match `rails`. That'll include gems like `rspec-rails` and
+`sprockets-rails`.
+
+First, the `--exact` flag can be added to narrow down the results to an exact
+match of `rails`.
+
+Then, the `--remote` flag can be included to request `gem` look for remote
+versions. That is, versions available on the rubygems server.
+
+Lastly, the `--all` flag can be included to fetch all versions instead of only
+the latest version.
+
+Putting it all together:
+
+```bash
+$ gem list rails --exact --remote --all
+rails (6.1.0, 6.0.3.4, 6.0.3.3, ... 0.9.0, 0.8.5, 0.8.0)
+```
+
+[source](https://stackoverflow.com/a/9146057/535590)