This is the code I am running, it does fine until I get to line 15. The command I run is: ruby ex16.rb text.txt. This is a practice sample I'm writing which is meant to be a simple little text editor: filename = ARGV.first script = $0 puts "We're going to erase #{filename}." puts "if you don't want that, hit CTRL-C (^C)." puts "If you do want that, hit RETURN." print "? " STDIN.gets puts "Opening the file..." target = File.open(filename, 'w') puts "Truncating the file. Goodbye!" target.truncate(target.size) puts "Now I'm going to ask you for three lines." print "line 1: "; line1 = STDIN.gets.chomp() print "line 2: "; line2 = STDIN.gets.chomp() print "line 3: "; line3 = STDIN.gets.chomp()undefined method 'size' puts "I'm going to write these to the file." target.write(line1) target.write("\n") target.write(line2) target.write("\n") target.write(line3) target.write("\n") puts "And finally, we close it." target.close()