Diff two sorted files

diff-sorted.rb

#!/bin/ruby

def trace(old, new)
	printf "%p old=%p new=%p\n", caller[0], old, new
end

def fetch(io)
	s = io.gets and s.chomp!
	s
end

def cmp(old, new)
	if old.nil? || (new && old > new)
		return '+', new
	elsif new.nil? || (old && old < new)
		return '-', old
	else
		return ' ', old
	end
end

old_file, new_file = ARGV.shift 2

File.open old_file do |of|
	File.open new_file do |nf|
		r_old = fetch(of)
		r_new = fetch(nf)

		begin
			#trace r_old, r_new
			flag, s = cmp(r_old, r_new)
			printf "%s%s\n", flag, s
			
			case flag
			when '-'
				r_old = fetch(of)
			when '+'
				r_new = fetch(nf)
			when ' '
				r_old = fetch(of)
				r_new = fetch(nf)
			else
				raise 'programmer error'
			end
		end while r_old || r_new
	end
end