From: James Edward Gray II <james@...>
Date: 2006-03-24T07:13:42+09:00
Subject: Re: variable substitution in strings read from a file

On Mar 23, 2006, at 3:31 PM, Stephen Bannasch wrote:

> I have a bunch of template documents which I need to manipulate in  
> very simple ways. I'd like to be able to insert Ruby variables into  
> the template. Here is a very short example:
>
> file fruit_template.txt: This is a fruit: #{fruit}.
>
> fruit = "apple"
> f = IO.read("fruit_template.txt")
>
> Then somehow I'd like to end up with this string:
> "This is a fruit: apple."

The easy answer to your question is to use eval():

 >> fruit = "apple"
=> "apple"
 >> f = 'This is a fruit: #{fruit}.'
=> "This is a fruit: \#{fruit}."
 >> eval %Q{"#{f}"}
=> "This is a fruit: apple."

The right answer is to use a template library, like the standard ERB:

 >> f = "This is a fruit:  <%= fruit %>."
=> "This is a fruit:  <%= fruit %>."
 >> require "erb"
=> true
 >> ERB.new(f).result(binding)
=> "This is a fruit:  apple."

Hope that helps.

James Edward Gray II