What does %{} do in Ruby?

Question

In Matt's post about drying up cucumber tests, Aslak suggests the following.

When I have lots of quotes, I prefer this:

Given %{I enter “#{User.first.username}” in “username”}

What is the %{CONTENT} construct called? Will someone mind referencing it in some documentation? I'm not sure how to go about looking it up.

There's also the stuff about %Q. Is that equivalent to just %? What of the curly braces? Can you use square braces? Do they function differently?

Finally, what is the #{<ruby stuff to be evaluated>} construct called? Is there a reference to that in documentation somewhere, too?

Answer 1

None of the other answers actually answer the question.

This is percent sign notation. The percent sign indicates that the next character is a literal delimiter, and you can use any (non alphanumeric) one you want. For example:

%{stuff} %[stuff] %?stuff? 

etc. This allows you to put double quotes, single quotes etc into the string without escaping:

%{foo='bar with embedded "baz"'} 

returns the literal string: foo='bar with embedded "baz"'

The percent sign can be followed by a letter modifier to determine how the string is interpolated. For example, %Q[ ] is an interpolated String, %q[ ] is a non-interpolated String, %i[ ] is a non-interpolated Array of Symbols etc. So for example:

 %i#potato tuna# 

returns this array of Symbols:

[:potato, :tuna] 

Details are here: Wikibooks