Question

I want to check a string and change any @something to link. So I have a helper function which consists of something like this:

def parse(content)
  content.gsub(/@[a-zA-z0-9]+\b/, link_to("#{$1}", user_path($1)) )
end

But the result is <a href="/users/102"></a>

The problem is :

1. The <a href="/users/102"></a> is a string, because somehow the < and > is escaped.
2. Why does "#{$1}" return nothing? Isn’t it supposed to return whatever is checked upon, in this case @something?

Answer 1

1. Rails HTML-escapes any content produced by a user-defined helper, unless you tell it not to. Try using <%= raw parse(content) %> in your view.
2. Quoting Pickaxe on gsub:

If a string is used as the replacement, special variables from the match (such as $& and $1)
cannot be substituted into it, because substitution into the string occurs before the pattern match
starts. However, the sequences \1, \2, and so on, may be used to interpolate successive numbered
groups in the match, and \k<name> will substitute the corresponding named captures.

So you can’t use #{$1} because $1 isn’t set until after the command has finished. Your best bet is probably to use the block form of gsub – in which case $1 is set inside the block. Try:

def parse(content)
  content.gsub(/@[a-zA-z0-9]+\b/) {link_to($1, user_path($1))} 
end