Add Read The First Line From A File 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://tinyletter.com/jbranchaud).
 
-_1062 TILs and counting..._
+_1063 TILs and counting..._
 
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@@ -884,6 +884,7 @@ _1062 TILs and counting..._
 - [Percent Notation](ruby/percent-notation.md)
 - [Question Mark Operator](ruby/question-mark-operator.md)
 - [Rake Only Lists Tasks With Descriptions](ruby/rake-only-lists-tasks-with-descriptions.md)
+- [Read The First Line From A File](ruby/read-the-first-line-from-a-file.md)
 - [Rendering ERB](ruby/rendering-erb.md)
 - [Replace The Current Process With An External Command](ruby/replace-the-current-process-with-an-external-command.md)
 - [Require Entire Gemfile In Pry Session](ruby/require-entire-gemfile-in-pry-session.md)

ruby/read-the-first-line-from-a-file.md

@@ -0,0 +1,33 @@
+# Read The First Line From A File
+
+If I wanted to read the first line from a file with Ruby, I'd probably read the
+whole thing in, split it by newlines, and grab the first.
+
+```ruby
+File.read('README.md').split(/\n/).first
+```
+
+This is inefficient in that it reads in the entire file. For small files this
+won't matter, but for larger files it could become a bottleneck.
+
+There is a method of doing this that is just as concise and streams the first
+part of the file rather than reading it in its entirety. The `File.open` method
+takes a block. This means you can pass a symbol-to-proc to it as the block
+argument.
+
+```ruby
+> File.open('README.md', &:readline).strip
+=> "# TIL"
+> File.open('README.md', &:gets).strip
+=> "# TIL"
+```
+
+Both `#readline` and `#gets` will grab the first line including the newline
+character (hence the `#strip`). The only difference is that `#readline` will
+raise an exception if the file is empty.
+
+These methods both come from the `IO` module and [stream the file rather than
+slurping the whole thing
+in](https://blog.appsignal.com/2018/07/10/ruby-magic-slurping-and-streaming-files.html).
+
+[source](https://stackoverflow.com/questions/1490138/reading-the-first-line-of-a-file-in-ruby)