generate subscript in controller and pass to view - html

Question

In controller, I can pass string to view.
How can I pass string with subscript?
In html its easy, just use a <sub> tag.
I tried 3 times to pass this subscript to view but failed.
If I pass <sub> inside the string, it will display I<sub>tag</sub> instead of Itag.
If I use string1="string"+<sub>+"tag"+</sub> ,and pass
string1, The controller will give error!
Last, I tried directly to copy subscript string inside the page, I
also got an error that it can't get displayed.
How can I pass subscript string to view? I got to loop different conditions so I cant each use <sub> tag, I need pass from controller.
Edit:
I tried this code in controller
#valuedisplay=#value.to_s + " m/s<sup>2</sup>".html_safe
As suggest solution ,and I get:
Just as what I said in 1st try,display the <sup> instead of m2.
If I do it in view,I have many different types of data ,I need add checking data type code in view according to different types,its doable but will make the view messy, I felt there should be a neat way to settle it in controller?

Answer 1

You need to safely render the HTML in your view, and for this purpose, you need to call html_safe function on your string:
#str = "I<sub>tag</sub>".html_safe
And, now when you pass this #str to your view, it will render the #str as expected.
In view:
<%= #str %>
Caution:
It would be a very bad practice to do so. <sub>ag</sub> belongs to view, so it should be in view. You can do something like following:
In controller:
#str = "tag"
And in view:
I<sub><%= #str %></sub>
<%# or %>
<%= "I<sub>#{#str}</sub>" %>