Add Extract Capture Group Matches With String Slices as a Ruby TIL

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
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@@ -1279,6 +1279,7 @@ See some of the other learning resources I work on:
 - [Exit A Process With An Error Message](ruby/exit-a-process-with-an-error-message.md)
 - [Expect A Method To Be Called And Actually Call It](ruby/expect-a-method-to-be-called-and-actually-call-it.md)
 - [Extract A Column Of Data From A CSV File](ruby/extract-a-column-of-data-from-a-csv-file.md)
+- [Extract Capture Group Matches With String Slices](ruby/extract-capture-group-matches-with-string-slices.md)
 - [FactoryGirl Sequences](ruby/factory-girl-sequences.md)
 - [Fail](ruby/fail.md)
 - [Fetch Warns About Superseding Block Argument](ruby/fetch-warns-about-superseding-block-argument.md)

ruby/extract-capture-group-matches-with-string-slices.md

@@ -0,0 +1,37 @@
+# Extract Capture Group Matches With String Slices
+
+Ruby's _string slice_ syntax allows us to use the square brackets to access
+portions of a string. It's most common to pass positional integer index
+arguments or a range. However, in true Ruby fashion, another way of thinking
+about defining the slice of a string is based on a regex match.
+
+We can pass a regex and an int (specifying which match we want) to extract some
+portion of a string based on the regex match. That includes capture groups.
+
+Here are a couple examples of extracting matching capture groups as well as
+getting the entire regex match:
+
+```ruby
+> "me+abc123@email.com"[/.+\+(.+)@(.+)/, 1]
+=> "abc123"
+
+> "me+abc123@email.com"[/.+\+(.+)@(.+)/, 2]
+=> "email.com"
+
+> "me+abc123@email.com"[/.+\+(.+)@(.+)/, 0]
+=> "me+abc123@email.com"
+
+> "me+abc123@email.com"[/.+\+(.+)@(.+)/]
+=> "me+abc123@email.com"
+```
+
+The `0`th match (which is the default) corresponds to the full match. Each
+integer position after that corresponds to any capture groups. This maps
+directly to the underlying `MatchData` object:
+
+```ruby
+> /.+\+(.+)@(.+)/.match("me+abc123@email.com")
+=> #<MatchData "me+abc123@email.com" 1:"abc123" 2:"email.com">
+```
+
+[source](https://ruby-doc.org/3.3.6/String.html#class-String-label-String+Slices)