Get rid of duplication from 2 files

exec.rb

input = []
File.foreach("input.txt"){|line|
    input << line.chomp
}

output = []
File.foreach("output.txt"){|line|
    output << line.chomp
}
// Remove duplicated entries in input from output
result = input - output

File.open("result.txt", "w") do |f|
    result.each { |s| f.puts(s) }
end