Indent Multiline String in Erb

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: 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"

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.

How to print a string in erb file including line breaks

Since you tagged this question with ruby-on-rails I guess you want to output to a webpage. I would recommend this:

<%= simple_format(str) %>

Form the docs:

simple_format("Here is some basic text...\n...with a line break.")
# => "<p>Here is some basic text...\n<br />...with a line break.</p>"

Building multi-line strings, programmatically, in Ruby

This would be one way:

code = []
code << "next line of code #{something}"
code << "another line #{some_included_expression}"
code.join("\n")

Rails 3: Why does an indent appear when repopulating text_areas with line breaks?

Ok, the problem seemed to be the mix between html.haml and html.erb views in the application. So either the .erb views are not properly rendered, or they don't play nice with the other .haml views. In mi case, for example, the application layout view is in haml, but the form was in erb.

Whatever the cause, the bottom line is that the text_area_tags don't render correctly in erb, but do in haml. So my workaround, although I know it is very hacky and not pretty, was to make a small partial in haml called _text_area.html.haml which renders just the textarea for a form:

_text_area.html.haml:

-if defined? options
    = f.text_area field, options
-else
    = f.text_area field

So every time I want to have a text_area tag in a form, I have to call a render like so:

<%= form_for @instance do |f| %>
    ...
    <%= render :partial => 'common/text_area', :locals => {:f => f, :field => :some_field_from_instance, :options => {:cols => 40, :rows => 10}} %>
    <%= render :partial => 'common/text_area', :locals => {:f => f, :field => :some_other_field} %>
    ...
<% end %>

This renders perfectly. That's why I think the problem lies with haml and its interpretation of indentation. If anyone has a better solution, please do let me know.

Looping over a string adds white space between characters in Ruby

Actually I then searched a more Ruby on Rails like solution, than above, so this then works for me to show any #word as a link, and it is much more simple.

<div class='tweet-text'>                
    <%= highlight(feed.text, /#\w+/, highlighter: '<a href="search?q=\1">\1</a>') %>
</div>