Best way to add comments in erb

Question

How do we add comments in erb files, if we do not want them to be generated into the html content?

score 398 · Accepted Answer · answered May 05 '10 at 15:59

398

Use the <%# %> sequence, e.g.

<%# This is a great comment! %>

answered May 05 '10 at 15:59

John Douthat

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I used to use this format until I noticed it just raised an error on someones computer in my team (we were both using linux, but different distros), regardless I avoid it since.. – vise May 05 '10 at 21:57
4

It's one of only a few supported ERB tags. http://www.ruby-doc.org/stdlib/libdoc/erb/rdoc/classes/ERB.html If it didn't work on their PC, they either had a typo, or they weren't using real ERB. However, I've run into issues with code like this <% for foo in bar # loop over bar %>.. This was OK in the ERB that shipped with 1.8.6, but when I switched to 1.8.7, it caused lots of problems. – John Douthat May 05 '10 at 22:20
23

i.e. there can't be any space between `<%` and `#` – John Douthat May 05 '10 at 22:30
How can i get textmate to generate these style of comments with apple-/ – Michael Aug 10 '10 at 22:39
2

@Mike Ctrl+Shift+Period (i.e. Ctrl+GreaterThan) 4 times quickly should do it. – John Douthat Aug 11 '10 at 16:02
This occasionally fails in some rubys... I find you need to put the closing "%>" tag on a newline... which feels a bit kludgy, but means you don't suddenly find half your template disappears on production, even though it works find on development :P – Taryn East Nov 07 '11 at 15:55
@TarynEast: be sure there aren't any characters between `<%` and `#` – John Douthat Nov 07 '11 at 18:13
I have some problem commenting this
<%= link_to "News", news_path %>
<%= link_to "News", news_path %>

WowBow

Jun 10 '12 at 20:26

By the way, for those using sublimetext2 .. check out https://github.com/eddorre/SublimeERB – Abram Dec 27 '12 at 03:25

I was using this but found it doesn't work if I want to comment out a section of existing code that already contains a closing tag %> (because the comment ends at the first closing tag). So now I'm using the <% if false %> <%end%> suggestion by user user3212755. Does anyone have any other suggestions? – TMin Feb 14 '15 at 16:38

score 53 · Answer 2 · answered May 05 '10 at 16:25

53

For Record

<%# This is a great comment! %>

<%#= This is a great comment! %>

answered May 05 '10 at 16:25

Salil

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The `<%=` -> `<%#=` example is useful. It doesn't require a special case and [isn't documented](http://ruby-doc.org/stdlib-1.9.3/libdoc/erb/rdoc/ERB.html). It works and is the easiest, though! (Beats having to guess whether there was an `=` when uncommenting it.) – Benjamin Atkin Mar 04 '12 at 18:52
3

What's the difference between the two? – Travis Reeder Jan 04 '17 at 14:09
5

@TravisR: The first one is just a comment, the second is also just a comment but probably arises when you're trying to disable a `<%= ... %>` by turning it into a comment. – mu is too short Aug 07 '17 at 04:00
Here's more info on [What is the difference difference between '<%#' and '<%#=' in ERB comments?](https://stackoverflow.com/questions/45538995/what-is-the-difference-difference-between-and-in-erb-comments?noredirect=1&lq=1) – sb813322 Dec 30 '22 at 09:09

Tim · Answer 3 · 2014-01-19T18:08:52.493

35

For block comments:

<% if false %>
    code to be commented out...
<% end %>

edited Jan 19 '14 at 18:08

answered Jan 19 '14 at 18:03

Tim

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For blocks you can just add line breaks inside the `<%# %>` tag. – RobW Jul 07 '16 at 18:54
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Would probably still give errors for broken code in the comment – Qwertie Jul 31 '17 at 01:40

score 7 · Answer 4 · answered Oct 26 '11 at 18:56

7

I have a Windows setup, and this <%-# %> sequence is the only one that works for me:

Example:

<%-# This is a sample comment! %>

answered Oct 26 '11 at 18:56

Edward Castano

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score 4 · Answer 5 · answered May 30 '19 at 04:32

4

In my text editor, i run command + / (sublime-text shortcut). It will be like this.

<%
=begin%>
    Here is the comment 
<%
=end%>

It doesn't look simply, but it works.

answered May 30 '19 at 04:32

Miftah Mizwar

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This works as hoped in .ERB files where one wants to comment out multiple statements all at once. An explanation of what is actually happening would be a good addition to the answer. – RARay Oct 07 '20 at 20:54
what is `command` in this context? – Aiden Cullo Aug 18 '23 at 16:51

score 2 · Answer 6 · edited Aug 22 '23 at 22:44

2

Since .erb is "embedded ruby" by definition, you can embed any ruby code between: <%= and the other: %>, typically all written in one line. In addition, ruby one-line comments start always with #, so the <%=# Comment %> style matches perfectly with both pure-ruby and erb styles for one-line comments.

edited Aug 22 '23 at 22:44

nullromo

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answered Feb 05 '15 at 10:36

Maaaaaaarco

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This does not work `
">
` throws an error – Epigene Feb 26 '15 at 11:14
1

@Epigene Likely cause of the error is the inner quotes. Not sure why you'd want to do this, but to get rid of the error, try: `value="<%=# 'String' %>"` – jdigital Nov 15 '15 at 04:59

Arezki · Answer 7 · 2019-03-27T21:31:04.623

1

I doesn't work in the Controllers files, I had to put it between slashes

/ comment here.... /

edited Mar 27 '19 at 21:31

answered Mar 27 '19 at 21:20

Arezki

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Aiden Cullo · Answer 8 · 2023-08-18T16:58:21.257

0

For .html.erb files, you can use the standard HTML multi-line comment

<!-- 
...erb and html code...
-->

For example,

<!--
<div>
  <%= form.label :book_id, style: "display: block" %>
  <%= form.text_field :book_id %>
</div>
-->

It also works for a single line,

<!-- <%= 1 %> -->

edited Aug 18 '23 at 16:58

answered Aug 10 '23 at 19:25

Aiden Cullo

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Best way to add comments in erb

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