#Assuming you have svn.log (the output of svn log) and line_counts.txt (a file which has a mapping of svn revision numbers to line counts), this will take the highest revision number in each month and tell you how many lines were in it.

grep r[0-9][0-9]* svn.log | ruby -e 'require "rubygems"; require "active_support"; counts = {}; STDIN.readlines.map {|r| r.split(" | ").map {|a| a.strip}}.map {|r| d = Date.parse(r[2]).beginning_of_month; rr = r[0].sub("r", ""); counts[d] = rr if (counts[d].nil? || counts[d] < rr)}; END { counts.to_a.sort {|a,b| a[0] <=> b[0]}.map {|a| puts "#{a[0].year}-#{a[0].month} #{a[1]}"}}' > highest_revisions.txt

ruby -e 'require "date"; revs = File.readlines("highest_revisions.txt").map {|a| a.split(" ")}.inject({}) {|acc, a| acc[a[0]] = a[1]; acc}; lines = File.readlines("line_counts.txt").map {|a| a.split(" ")}.inject({}) {|acc, a| acc[a[0]] = a[1]; acc}; lines2 = {}; revs.to_a.each {|a| lines2[a[0]] = lines[a[1]]}; lines2.to_a.sort {|a,b| Date.parse(a[0] + "-01")<=>Date.parse(b[0] + "-01")}.map {|a| puts "#{a[0]} #{a[1]}"}'