my lint based, error checking pre-commit

gistfile1.rb

#!/usr/bin/env ruby
#
# A hook script to verify that only syntactically valid ruby code is commited.
# Called by git-commit with no arguments. The hook should
# exit with non-zero status after issuing an appropriate message if
# it wants to stop the commit.
#
# Put this code into a file called "pre-commit" inside your .git/hooks
# directory, and make sure it is executable ("chmod +x .git/hooks/pre-commit")

puts "in .git/hooks/pre-commit"

require 'open3'
include Open3

# Set this to true if you want warnings to stop your commit
stop_on_warnings = false
stop_on_errors = true

# compiler_ruby = `which rbx`.strip
# compiler_ruby = `which ruby`.strip if compiler_ruby.length == 0

# setting compiler to ruby-1.9.3 since `which ruby` was setting it to 1.8.7
compiler_ruby = "$HOME/.rvm/rubies/ruby-1.9.3-p484/bin/ruby"

changed_ruby_files = `git diff-index --name-only --cached HEAD`.split("\n").inject([]) do |files, line|
  files << line.chomp if line =~ /(.+\.(e?rb|task|rake|thor)|[Rr]akefile|[Tt]horfile)/
  files
end

problematic_files = changed_ruby_files.inject([]) do |problematic_files, file|
  if File.readable? file
    cmd = if file =~ /\.erb\z/
      # Set trim mode to "-", just as Rails does
      # Replacing all <%= tags with <% for the syntax check
      "sed 's/<%=/<%/g' #{file} | erb -xT - | #{compiler_ruby} -wc"
    else
      "#{compiler_ruby} -wc #{file}"
    end

    errors = nil
    popen3(cmd) do |stdin, stdout, stderr|
      errors = stderr.read.split("\n")
    end

    errors.reject!{ |line| line =~ /[0-9]+:\s+warning:/ } unless stop_on_warnings
    errors.reject!{ |line| line =~ /[0-9]+:\s+syntax error/ } unless stop_on_errors

    unless errors.empty?
      errors.map!{ |line| line.sub(/#{file}:/, '') }
      problematic_files << "#{file}:\n#{errors.join("\n")}"
    end
  end

  problematic_files
end

if problematic_files.size > 0
  $stderr.puts problematic_files.join("\n\n")
  exit 1
else
  puts "no syntax errors"
  # All is well
  exit 0
end