Report non-ASCII characters in a file

ascii_only.rb

#!/usr/bin/env ruby

# x starts at 0 because we increment x BEFORE checking the character.
# y starts at 1 because we only increment it when we hit a newline.
x, y = 0, 1

puts 'Positions are 1-indexed, NOT 0-indexed.'
puts 'i.e. The first character in the file is at position 1:1'
puts

File.read(ARGV[0]).split('').each do |char|
  x += 1
  puts "#{char} at #{y}:#{x} is not an ASCII character" unless char.ascii_only?
  if char == "\n"
    x = 0
    y += 1
  end
end