Question

>> string = '#{var}'
=> "\#{var}"

>> proc = Proc.new { |var| string }
=> #<Proc:0xb717a8c4@(pry):6>

>> proc.call(123)
=> "\#{var}"

Not really what I want. Double quotes around string result in the obvious undefined local variable.

Answer 1

Although this is possible, it’s not going to work how you intend here without having to use eval, and generally that’s a bad idea if there’s an alternative. The good news is you have several options.

The most straightforward is to use sprintf formatting which is made even easier with the String#% method:

string = '%s'

proc = Proc.new { |var| string % var }

proc.call(123)
# => "123"

This is a really reliable method as anything that supports the .to_s method will work and won’t cause the universe to implode if it contains executable code.