Difference between -%> and %> in rails

Question

I have started some rails tutorials and noticed that some of the view code blocks are like

<h1><%= @subject.name -%></h1>

and other code blocks are like

<h1><%= @subject.name %></h1>

What is the difference between -%> and %>

If you know of some good syntax references you can point me to, that would also be helpful.

This one was asked before the referenced one was. Though I trust our moderators know what they are doing. — Brettski, Sep 03 '14 at 16:51

score 88 · Accepted Answer · answered Jun 15 '09 at 23:44

88

The extra dash makes ERB not output the newline after the closing tag. There's no difference in your example, but if you have something like this:

<div>
  <% if true -%>
  Hi
  <% end -%>
</div>

It'll produce:

<div>
  Hi
</div>

and not this:

<div>

  Hi

</div>

answered Jun 15 '09 at 23:44

zenazn

14,295
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Thank you so much! I found this by first by finding a search engine that allows for special characters, and then by searching for -%>. This was the first page that showed up. I used http://www.symbolhound.com/ (and I'm probably going to be using it quite often now, because it's IMPOSSIBLE to search for special symbols on Google). – Andrew Larsson May 04 '12 at 18:10
4

Make sure when using ERB in a standalone ruby script to pass the `trim_mode` to `ERB.new`, e.g. `ERB.new('myfile.erb', nil, '-')` where `'-'` is the `trim_mode`, otherwise it won't accept the dashes – Koen. Sep 18 '12 at 10:18
This slipped me up when trying to pipe to the `erb` command line tool. As @Koen. stated setting trim mode fixes the issue and the command has an option to set it i.e. (`erb -T '-'`). – erran Oct 30 '14 at 04:22

score 5 · Answer 2 · answered Apr 16 '13 at 23:06

5

I'm pretty sure - before %> is no longer necessary, and should be left out.

At least in Chrome, the generated html looks the same using -%> or %>.

answered Apr 16 '13 at 23:06

gylaz

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I do not reproduce neither in pure Ruby 2.1 nor Rails 4.1: to remove the newline I either need `-`, or `trim_mode` `<>` (which Rails does not seem to set by default). – Ciro Santilli OurBigBook.com Sep 02 '14 at 07:12

score 4 · Answer 3 · answered Jun 16 '09 at 08:39

If you use HAML rather than ERB you can do something similar with a less than or greater symbol than after your tag.

> will remove any whitespace around your tag and < will remove any whitespace within it.

.float-left<
  %p
    Lorem ipsum dolor sit amet

is compiled to:

<div class="float-left"><p>
  Lorem ipsum dolor sit amet
</p></div>

And…

%left_tag
%inside>
%right_tag

is compiled to:

<left_tag /><inside /><right_tag />

If you're not using HAML it's definitely worth checking out.

score 3 · Answer 4 · edited May 23 '17 at 12:34

UPDATE: This answer was wrong, see https://stackoverflow.com/a/25626629/895245 instead.

In Ruby 2.1 (not necessarily with Rails), the - removes one trailing newline:

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 documents this at http://api.rubyonrails.org/classes/ActionView/Base.html, and 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

However, Rails 4.1 does remove trailing whitespaces as documented while pure ERB does not, so there may be other differences.

Also, it is not removing the leading newlines as documented: it might be a documentation bug. Opened an issue at: https://github.com/rails/rails/issues/16766

Wee gist to demonstrate trim level differences between ERB and Erubis: https://gist.github.com/mikecmpbll/72a32f79dc3821e9d2a8 — Mike Campbell, Nov 13 '14 at 13:51

Difference between -%> and %> in rails

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