n2s.rb

def process(file)
  text = File.read(file)
  string = text.lines.first
  string.split(', ')
    .map {|c| c.split("=")}
    .inject({}) {|c, v| c[v[0]]=v[1].to_s.split(" ").map(&:to_i); c}
    .inject([]) {|k, v| v[1].each {|i| k[i] = v[0]}; k}
    .join
end

Dir["files/*.txt"].each do |file|
 puts process(file)
end

# Consider for readability

def decode(file)
  File
    .open(file, "r") { |f| f.read }
    .split("\n")[0]
    .split(", ")
    .map { |line| line.split("= ") }
    .inject({}) { |hash, (char, string_of_numbers)| hash[char] = string_of_numbers.to_s.split(" ").map(&:to_i) ; hash }
    .inject([]) { |array, (char, indices)| indices.map { |i| array[i] = char } ; array }
    .join
end

p decode("./ccw5ccwf.txt")