ruby

#!/usr/bin/env ruby
class FileDiffExtractor
  DIFF_HUNK_REGEX = /
      ^@@\s
      [^\s]+\s           # Ignore old file range
      \+(\d+)(?:,(\d+))? # Extract range of hunk containing start line and number of lines
      \s@@.*$
    /x

  def call
    modified_files.each do |name|
      File.open(name, "r") do |f|
        `git diff --no-color --no-ext-diff -U0 --cached -- "#{name}"`.
          scan(DIFF_HUNK_REGEX) do |start_line, lines_added|
          lines_added = (lines_added || 0).to_i
          start_line = start_line.to_i

          f.each_line.with_index(1) do |e, i|
            next unless i.between?(start_line, start_line + lines_added)
            next if e == "\n" || e == ''
            puts e
          end
        end
      end
    end
  end

  def modified_files
    `git diff --name-only -z --diff-filter=ACMR --ignore-submodules=all --cached`.
      split("\0").
      map(&:strip).
      reject(&:empty?).
      map { |relative_file| File.expand_path(relative_file) }
  end
end

FileDiffExtractor.new.call