From: "Bartosz Dziewoński" <matma.rex@...>
Date: 2012-12-15T04:52:00+09:00
Subject: Re: Invoking bash from Ruby

Yes; use string interpolation to insert the variable's content into the string:

foo = 'world'
puts "Hello, #{foo}!" # outputs: Hello, world!

It works the same for backticks and the percent string-like notation
(but you'll have to use %X with uppercased X, similarly to how you
have to use strings in quotes instead of in apostrophes to be able to
interpolate in them).

So this would be (note: code untested):

date = %X{grep "<strong>Date:</strong>" #{fn} | cut -d' ' -f3-5}

Also, if the contents of fn come from the user, you should escape it
somehow to prevent them from executing arbitrary commands in your
shell environment!

-- Matma Rex