In Ruby, can you perform string interpolation on data read from a file?

Question

In Ruby you can reference variables inside strings and they are interpolated at runtime.

For example if you declare a variable foo equals \"Ted\

Answer 1

Using daniel-lucraft's answer as my base (as he seems to be the only one that answered the question) I decided to solve this problem in a robust manner. Below you will find the code for this solution.

# encoding: utf-8

class String
  INTERPOLATE_DELIMETER_LIST = [ '"', "'", "\x02", "\x03", "\x7F", '|', '+', '-' ]
  def interpolate(data = {})
    binding = Kernel.binding

    data.each do |k, v|
      binding.local_variable_set(k, v)
    end

    delemeter = nil
    INTERPOLATE_DELIMETER_LIST.each do |k|
      next if self.include? k
      delemeter = k
      break
    end
    raise ArgumentError, "String contains all the reserved characters" unless delemeter
    e = s = delemeter
    string = "%Q#{s}" + self + "#{e}"
    binding.eval string
  end
end

output =
begin
  File.read("data.txt").interpolate(foo: 3)
rescue NameError => error
  puts error
rescue ArgumentError => error
  puts error
end

p output

for the input

he #{foo} he

you get the output

 "he 3 he"

The input

"he #{bad} he\n"

will raise a NameError exception. And the input

"\"'\u0002\u0003\u007F|+-"

will raise and ArgumentError exception complaining that the input contained all available delimiter characters.

Answer 2

Well, I second stesch's answer of using erb in this situation. But you can use eval like this. If data.txt has contents:

he #{foo} he

Then you can load and interpolate like this:

str = File.read("data.txt")
foo = 3
result = eval("\"" + str + "\"")

And result will be:

"he 3 he"