Ruby Indented Multiline Strings

Multiline strings with no indent

In the RubyTapas Episode 249, Avdi Grimm describes a technique to strip leading whitespace from a multi-line string:

def unindent(s)
  s.gsub(/^#{s.scan(/^[ \t]+(?=\S)/).min}/, '')
end

It is behavior compatible to other existing solutions to this problem, e.g. String#strip_heredoc in ActiveSupport / Rails or the standalone unindent gem.

You can use this method with a heredoc which is special syntax in ruby (and many other languages) to write multi-line strings.

module Something
  def unindent(s)
    s.gsub(/^#{s.scan(/^[ \t]+(?=\S)/).min}/, '')
  end

  def welcome
    unindent(<<-TEXT)
      Hello

      This is an example. This multiline string works
        - even with deeper nestings...
      All is OK here :)
    TEXT
  end
end

Is there an easy way to do multiline indented strings in Ruby?

Since Ruby 2.3, the <<~ heredoc strips leading content whitespace:

def make_doc(body)
  <<~EOF
  <html>
    <body>
      #{body}
    </body>
  </html>
  EOF
end

puts make_doc('hello')

For older Ruby versions, the following is more verbose than the solutions presented in the other answers, but there's almost no performance overhead.
It's about as fast as a single long string literal:

def make_doc(body)
  "<html>\n"       \
  "  <body>\n"     \
  "    #{body}\n"  \
  "  </body>\n"    \
  "</html>"
end

Ruby indented multiline strings

Personally, I think that Ruby's indented heredocs are useless and they should work more like Bash indented heredocs and also strip whitespace inside the string …

Anyway, there are a couple of libraries that try to deal with this situation. There is a wide array of libraries that try to fix this problem:

Martin Aumont's Unindent library which is also part of the Facets library
Facets also provides String#margin
Sunlight Labs' Unindentable library
Samuel Dana's Indentation library

Ruby: Can I write multi-line string with no concatenation?

There are pieces to this answer that helped me get what I needed (easy multi-line concatenation WITHOUT extra whitespace), but since none of the actual answers had it, I'm compiling them here:

str = 'this is a multi-line string'\
  ' using implicit concatenation'\
  ' to prevent spare \n\'s'

=> "this is a multi-line string using implicit concatenation to eliminate spare
\\n's"

As a bonus, here's a version using funny HEREDOC syntax (via this link):

p <<END_SQL.gsub(/\s+/, " ").strip
SELECT * FROM     users
         ORDER BY users.id DESC
END_SQL
# >> "SELECT * FROM users ORDER BY users.id DESC"

The latter would mostly be for situations that required more flexibility in the processing. I personally don't like it, it puts the processing in a weird place w.r.t. the string (i.e., in front of it, but using instance methods that usually come afterward), but it's there. Note that if you are indenting the last END_SQL identifier (which is common, since this is probably inside a function or module), you will need to use the hyphenated syntax (that is, p <<-END_SQL instead of p <<END_SQL). Otherwise, the indenting whitespace causes the identifier to be interpreted as a continuation of the string.

This doesn't save much typing, but it looks nicer than using + signs, to me.

Also (I say in an edit, several years later), if you're using Ruby 2.3+, the operator <<~ is also available, which removes extra indentation from the final string. You should be able to remove the .gsub invocation, in that case (although it might depend on both the starting indentation and your final needs).

EDIT: Adding one more:

p %{
SELECT * FROM     users
         ORDER BY users.id DESC
}.gsub(/\s+/, " ").strip
# >> "SELECT * FROM users ORDER BY users.id DESC"

Whitespace with multiline string in ruby

Ruby 2.3.0 solves this nicely with the squiggly heredoc. Note the difference of the tilde/hyphen between examples.

hyphen_heredoc = <<-MULTILINE_STRING
                    One line
                    Second line
                      Indented two spaces
                    MULTILINE_STRING

squiggly_heredoc = <<~MULTILINE_STRING_WITH_TILDE
                      One line
                      Second line
                        Indented two spaces
                      MULTILINE_STRING_WITH_TILDE

2.3.0 :001 > puts hyphen_heredoc
                      One line
                      Second line
                        Indented two spaces
2.3.0 :002 > puts squiggly_heredoc
One line
Second line
  Indented two spaces

With the squiggly heredoc, The indentation of the least-indented line will be removed from each line of the content.

Interpolate multiline string with correct indent

I woke up and saw this question and decided to make it a morning programming puzzle to solve. It was harder than I thought. I'm not thrilled with the API or the complexity, but I didn't want to spend any more time, and it does work. Maybe you'll find it useful. If not, perhaps it will at least inspire some other alternative approaches.

I do not know of any libraries or frameworks that meet your needs using plain Ruby Here Documents. Ruby 2.3 has a new feature that basically does what Rails' #strip_heredoc does, but I haven't used it and I don't know how it handles multi-line interpolation. Here is the Ruby code for my custom solution based on your use case (using Ruby 2.0):

https://gist.github.com/shock/1d269a91f938bf1a1c3cba3856bedf19

Breaking up long strings on multiple lines in Ruby without stripping newlines

Three years later, there is now a solution in Ruby 2.3: The squiggly heredoc.

class Subscription
  def warning_message
    <<~HEREDOC
      Subscription expiring soon!
      Your free trial will expire in #{days_until_expiration} days.
      Please update your billing information.
    HEREDOC
  end
end

Blog post link: https://infinum.co/the-capsized-eight/articles/multiline-strings-ruby-2-3-0-the-squiggly-heredoc

The indentation of the least-indented line will be
removed from each line of the content.