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:

> "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 0th 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:

> /.+\+(.+)@(.+)/.match("me+abc123@email.com")
=> #<MatchData "me+abc123@email.com" 1:"abc123" 2:"email.com">

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