How to define a multiline string in Ruby

Note: The following was tested with Ruby 2.6.6

Keyword: Heredoc

What is heredoc?

Heredoc is used for a form of multiline strings and preserves the line breaks and whitespace (including indentation) in the text.

How to define a heredoc in Ruby?

string = <<~HEREDOC
  How are you?
HEREDOC

• Start with <<- or <<~.

• The word HEREDOC can be replaced with any text, ex. SQL, HTMLetc.

• End with the word you have defined, ex. HEREDOC.

How to use string interpolation with a heredoc?

It's simple.

string = <<~HEREDOC
  How are you, #{User.first.name}?
HEREDOC
#=> "How are you, Lynn\n"

If you would like to disable the interpolation, you can put the single quotes around the heredoc name.

string = <<~'HEREDOC'
  How are you, #{User.first.name}?
HEREDOC
#=> "How are you, \#{User.first.name}?\n"

What's the difference between <<- and <<~?

<<-

string = <<-HEREDOC
  Today is a nice day.
HEREDOC
#=> "  Today is a nice day.\n"

<<~

string = <<~HEREDOC
  Today is a nice day.
HEREDOC
#=> "Today is a nice day.\n"

<<- will maintain the original indentation. Ruby 2.3 introduced the squiggly heredoc <<~ which can removes extra indentation.

How to remove an extra newline?

You might notice that there is a newline character \n at the end of the return value. If you would like to remove an extra newline, strip will be useful.

string = <<~HEREDOC.strip
  Today is a nice day.
HEREDOC
#=> "Today is a nice day."

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Reference

• https://en.wikipedia.org/wiki/Here_document

• https://www.rubyguides.com/2018/11/ruby-heredoc

• https://blog.saeloun.com/2020/04/08/heredoc-in-ruby-and-rails