List environment variables used by ruby script

list_env.rb

#!/bin/ruby

REGEX = Regexp.new('ENV\[\s*(\S.*?)\s*\]')


def report
  list = list_found
  if list.empty?
    puts 'No environment variables found'
  else
    list.each {|item| puts "#{item}\n"}
  end
end


def list_found
  file_contents = read_file(ARGV.first)
  matches = file_contents.scan(REGEX).flatten.uniq
  matches.reject! {|match| match != match.upcase}
  matches
end


def read_file(filename)
  abort('Error: Filename not specified') unless filename
  if File.exists?(filename)
    File.read(filename)
  else
    puts "Could not locate file named #{filename}"
    exit(-1)
  end
end

report