Create random plain text file

create_random_file.rb

# coding: utf-8

SIZE = ARGV.shift.to_i
FILENAME = ARGV.shift

if SIZE < 1 || FILENAME.nil?
  puts "Usage: ruby #{File.basename(__FILE__)} <size> <file>"
  exit 1
end

WIDTH = 80
NUM_FULL_LINES = SIZE / WIDTH
LAST_LINE_WIDTH = SIZE % WIDTH
CHARS = [('a'..'z'), ('A'..'Z'), ('0'..'9')].map { |r| r.to_a }.flatten.join

def create_random_line(width)
  line = ''
  (width - 1).times { line << CHARS[rand(CHARS.size)] } # minus one for newline
  line << "\n"
end

File.open(FILENAME, 'w') do |file|
  NUM_FULL_LINES.times { file.write(create_random_line(WIDTH)) }
  file.write(create_random_line(LAST_LINE_WIDTH)) if LAST_LINE_WIDTH > 0
end