a.md

1. Download git-fixws.rb to ~/bin/git-fixws.rb
2. chmod +x ~/bin/git-fixws.rb
3. git config --global alias.fixws '!ruby ~/bin/git-fixws.rb'

With a dirty tree, you can then run git fixws to have trailing whitespace removed.

git-fixws.rb

#!/usr/bin/env ruby

class File
  def self.binary?(file)
    s = (read(file, stat(file).blksize) || "").split(//)
    s.size > 0 && ((s.size - s.grep(" ".."~").size) / s.size.to_f) > 0.30
  end

  def self.fix_trailing_space(file)
    content = read(file)
    if content =~ /\r\n/
      p :crlf => file
    end

    content.gsub!(/[\t ]+$/, '')
    open(file, "w") { |f| f << content }
  end
end


if ARGV.empty?
  status = `git status`.split("\n")
  files = status.map do |e|
    e[/(modified|new file):\s*(.+?)$/, 2] || e[/renamed:.+->\s*(.+?)$/, 1]
  end.compact
else
  files = ARGV
end

abort "no modified files" if files.empty?

files.each do |file|
  next if !File.file?(file)

  if File.binary?(file)
    p :binary => file
  else
    p :fixing => file
    File.fix_trailing_space file.strip
  end
end