What is the use case for Ruby's %q / %Q quoting methods?

Question

I\'ve been reading through Thomas\' Programming Ruby 1.9 and came upon the alternative delimited single and double-quoting methods (%q / %Q). I\'ve known of the

Answer 1

They're extraordinarily useful for escaping HTML with JavaScript in it where you've already "run out" of quoting methods:

link = %q[link]

I've also found them to be very useful when working with multi-line SQL statements:

execute(%Q[
  INSERT INTO table_a (column_a)
    SELECT value
      FROM table_b
      WHERE key='value'
])

The advantage there is you don't need to pay attention to the type of quoting used within your query. It will work with either single, double, or both. They're also a lot less fuss than the HEREDOC style method.

Ruby provides other convenience methods like this such as %r which can construct regular expressions. That avoids slash-itis when trying to write one that handles stuff like http:// that would otherwise have to be escaped.