Meaning of #{ } in Ruby?

Question

The operation #{ } appears to be so fundamental that my Ruby book completely skips its definition. Can someone provide an explanation?

Answer 1

Why This Is a Good Question

This is a tough question to Google for unless you know the right search terms. The #{} operator technically performs expression substitution inside a string literal.

The Answer

The #{} literal is the operator used for interpolation inside double-quoted strings the same way that the backticks or $() construct would be used in Bash. From a practical point of view, the expression inside the literal is evaluated, and then the entire #{} expression (including both the operator and the expression it contains) is replaced in situ with the result.

Related Links

• http://www.ruby-doc.org/docs/ruby-doc-bundle/Manual/man-1.4/syntax.html#string
• http://www.ruby-doc.org/docs/ProgrammingRuby/html/language.html
• http://en.wikibooks.org/wiki/Ruby_Programming/Syntax/Literals#Interpolation
• Ruby (on Rails) syntax

Answer 2

It allows you to put Ruby code within a string. So:

"three plus three is #{3+3}" 

Would output:

"three plus three is 6"

It's commonly used to insert variable values into strings without having to mess around with string concatenation:

"Your username is #{user}"