Double Left Angle Bracket - Ruby Operator Lookup

There are a couple essential contexts in which you'll see << show up in Ruby. Head over to the Shift Operators page to see how else it is used.

Shovel Operator

Perhaps more commonly is as the Shovel Operator, which is conceptually used to "shovel" a value into a container. The more common term for this kind of action is append.

In the simplest case, the shovel operator is used to append a value to an array.

> items = [:a, :b]
=> [:a, :b]
> items << :c
=> [:a, :b, :c]
> items << [1,2,3]
=> [:a, :b, :c, [1, 2, 3]]
> items << true
=> [:a, :b, :c, [1, 2, 3], true]

heredoc

A heredoc (here document) is a way to create a multi-line string in Ruby. It's typically used for creating multi-line messages, SQL queries, or HTML.

There are several ways to define a heredoc, the most common being <<HEREDOC, <<-HEREDOC, and <<~HEREDOC.

A basic example of a heredoc is this:

query = <<SQL
  select *
  from users
  where active = true
    and role = 'admin'
SQL

execute(query)

If you're curious what the different forms do, head over to the heredoc page.