What does -%> mean in Ruby on Rails, compared to %>

Question

I've always used <%= some_code %> to insert Ruby into HTML when using Ruby on Rails. I've just noticed that other projects sometimes use <%= some_code -%>.

Superset question for all formats `<% %>` modifiers that came later: http://stackoverflow.com/questions/7996695/rails-erb-syntax — Ciro Santilli OurBigBook.com, Sep 01 '14 at 21:09
@CiroSantilli: You're dominating these - nice work! I picked http://stackoverflow.com/questions/7996695/what-is-the-difference-between-and-in-erb-in-rails for this one, too... — Brad Werth, Sep 02 '14 at 04:50

score 13 · Accepted Answer · answered Sep 27 '10 at 06:33

13

<%= some_code -%> The minus at the end removes the newline. Useful for formatting the generated HTML, while <%= some_code %> does not.

Thanks, Anubhaw

answered Sep 27 '10 at 06:33

Anubhaw

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What about the difference between starting with `<%=` vs `<%`? – Shawn Sep 15 '11 at 04:22
@ShawnSep `=` addes the output, `%` does not and is used for stuff like conditionals `<% if %>`. – Ciro Santilli OurBigBook.com Sep 01 '14 at 20:21

score 4 · Answer 2 · answered Sep 27 '10 at 07:03

4

It's delete on Rails 3.

Now with Rails 3, there are no difference between this 2 forms.

answered Sep 27 '10 at 07:03

shingara

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Not sure where you read that, but -%> still stops ERB from producing a trailing newline in rails 3. – Samuel Sep 27 '10 at 13:24
According to the Rails 3 release notes: "You no longer need to place a minus sign at the end of a ruby interpolation inside an ERb template to remove the trailing carriage return in the HTML output." – coder_tim Sep 27 '10 at 18:35
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@Tim That means it will remove the trailing CR from your HTML output, not from every line. -%> still exists and is still useful. – Samuel Sep 28 '10 at 18:36

score 1 · Answer 3 · edited May 23 '17 at 10:26

This answer was wrong: see https://stackoverflow.com/a/25617607/895245 instead.

In Ruby 2.1 (not necessarily with Rails), the - removes one following newline as pointed by Anubhaw:

the newline must be the first char after the >
no spaces are removed
only a single newline is removed
you must pass the '-' option to use it

Examples:

require 'erb'
ERB.new("<%= 'a' %>\nb").result              == "a\nb"  or raise
begin ERB.new("<%= 'a' -%>\nb").result; rescue SyntaxError ; else raise; end
ERB.new("<%= 'a'  %>\nb"  , nil, '-').result == "a\nb"  or raise
ERB.new("<%= 'a' -%>\nb"  , nil, '-').result == 'ab'    or raise
ERB.new("<%= 'a' -%> \nb" , nil, '-').result == "a \nb" or raise
ERB.new("<%= 'a' -%>\n b" , nil, '-').result == 'a b'   or raise
ERB.new("<%= 'a' -%>\n\nb", nil, '-').result == "a\nb"  or raise

Doc: http://ruby-doc.org/stdlib-2.1.1/libdoc/erb/rdoc/ERB.html

Rails 4.1 appears to:

use ERB by default at: https://github.com/rails/rails/blob/fcbdac7e82725c388bf5adf56a9a9a16d4efdbe0/actionview/lib/action_view/template/handlers.rb#L10
set - by default at: https://github.com/rails/rails/blob/fcbdac7e82725c388bf5adf56a9a9a16d4efdbe0/actionview/lib/action_view/template/handlers/erb.rb#L77

What does -%> mean in Ruby on Rails, compared to %>

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