Add Make An Executable Ruby Script as a Ruby 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://crafty-builder-6996.ck.page/e169c61186).
 
-_1223 TILs and counting..._
+_1225 TILs and counting..._
 
 ---
 
@@ -749,6 +749,7 @@ _1223 TILs and counting..._
 - [Get ActiveRecord Attribute Directly From Database](rails/get-active-record-attribute-directly-from-database.md)
 - [Get An Array Of Values From The Database](rails/get-an-array-of-values-from-the-database.md)
 - [Get An Empty ActiveRecord Relation](rails/get-an-empty-activerecord-relation.md)
+- [Get Help With A Rails App Update](rails/get-help-with-a-rails-app-update.md)
 - [Get The Column Names For A Model](rails/get-the-column-names-for-a-model.md)
 - [Get The Current Time](rails/get-the-current-time.md)
 - [Grab A Random Record From The Database](rails/grab-a-random-record-from-the-database.md)
@@ -1000,6 +1001,7 @@ _1223 TILs and counting..._
 - [Limit Split](ruby/limit-split.md)
 - [List The Running Ruby Version](ruby/list-the-running-ruby-version.md)
 - [Listing Local Variables](ruby/listing-local-variables.md)
+- [Make An Executable Ruby Script](ruby/make-an-executable-ruby-script.md)
 - [Map With Index Over An Array](ruby/map-with-index-over-an-array.md)
 - [Mock Method Chain Calls With RSpec](ruby/mock-method-chain-calls-with-rspec.md)
 - [Mocking Requests With Partial URIs Using Regex](ruby/mocking-requests-with-partial-uris-using-regex.md)

rails/get-help-with-a-rails-app-update.md

@@ -0,0 +1,29 @@
+# Get Help With A Rails App Update
+
+Rails version upgrades can be pretty involved. The ecosystem and the framework
+are under constant evolution. While each patch version will stay reliably
+stable, as soon as you go to do a minor or major upgrade (which you should stay
+on top of), you'll have lots to consider.
+
+Rails helps with this via the `app:update` rake task.
+
+When run, it will prompt you with a series of files that it wants to change.
+For each one you'll have some options.
+
+```bash
+$ rails app:update
+
+Overwrite my-app/config/boot.rb? (enter "h" for help) [Ynaqdhm]  h
+        Y - yes, overwrite
+        n - no, do not overwrite
+        a - all, overwrite this and all others
+        q - quit, abort
+        d - diff, show the differences between the old and the new
+        h - help, show this help
+        m - merge, run merge tool
+```
+
+Start by using `d` to see a diff of the changes. If it's small and doesn't
+overwrite important, existing settings, then you can use `y` to accept them.
+For a lot of these files the changes will be too aggressive. So side-by-side
+with the diff, update the file manually. Then use `n` to go to the next update.

ruby/make-an-executable-ruby-script.md

@@ -0,0 +1,38 @@
+# Make An Executable Ruby Script
+
+In a unix environment with Ruby available, I can make a Ruby script. To do this
+I stick some code in a Ruby file, like `database_url.rb`.
+
+```ruby
+result = `heroku pg:credentials:url DATABASE_URL --app my-app`
+puts result.split("\n")[2].strip
+```
+
+And then execute that file with `ruby`:
+
+```bash
+$ ruby database_url.rb
+```
+
+I can instead make an executable file that doesn't need to be explicitly
+invoked with the `ruby` command. To do this, I need to prefix my file with a
+[shebang](https://unix.stackexchange.com/a/87600/5916) for
+[`ruby`](https://devcenter.heroku.com/articles/ruby-binstub-shebang).
+
+And I'll even just call the file `database_url` now, no file suffix.
+
+```ruby
+#!/usr/bin/env ruby
+
+result = `heroku pg:credentials:url DATABASE_URL --app my-app`
+puts result.split("\n")[2].strip
+```
+
+When executed, this script will see the first line and understand that it needs
+to execute the rest of the script using `ruby` as the interpreter.
+
+Like any other executable, you can call it as is, like so:
+
+```ruby
+$ database_url
+```