old_contents: """Script to change -v for an ack command to vack"""
  
  import os
  import re
  import sys
  import commands
  
  def assert_perl_script(path):
      """Raise errors if that path is not a perl script
  
      It is a perl script if it
          1. is a file, and
          2.a. has a '.pl' extension, or
          2.b. mentions 'perl' in first line
      """
      if not os.path.isfile(path):
          #  I prefer string interpolation operator over format()
          raise NotImplementedError('"%s" is not a file' % path)
  
      stem, ext = os.path.splitext(path)
      if ext == '.pl':
          return
      with open(path) as stream:
          if 'perl' in stream.readline():
              return
      raise NotImplementedError('%s is not a perl script' % path)
  
  
  def which_ack():
      """Find the system 'ack' with which
  
      Should be a perl script
      """
      ack = os.environ.get('ACK') or 'ack'
      if not ack or not os.path.isfile(ack):
          status, output = commands.getstatusoutput('which ack')
          if status != os.EX_OK:
              raise NotImplementedError('"which ack" failed: "%s"' % output)
          ack = output
      assert_perl_script(ack)
      return ack
  
  def main(args):
      """Run this script as a program"""
      if '-U' in sys.argv:
          import pudb
          pudb.set_trace()
      words = [which_ack()]
      for word in args:
          if re.match('-[a-uw-z]*[vV][a-uw-z]*', word):
              words[0] = 'vack'
              words.append(word)
          else:
              if re.search('[.(]', word):
                  if ' $' in word:
                      words.append("'%s'" % word)
                  else:
                      words.append('"%s"' % word)
              else:
                  words.append(word)
      script = os.path.join(os.path.dirname(__file__), 'ack2vim.sh')
      words[0:0] = ('.', script, ';')
      print ' '.join(words)
  
  if __name__ == '__main__':
      sys.exit(main(sys.argv[1:]))
  
new_contents: """Script to change -v for an ack command to vack"""
  
  import os
  import re
  import sys
  import commands
  
  def assert_perl_script(path):
      """Raise errors if that path is not a perl script
  
      It is a perl script if it
          1. is a file, and
          2.a. has a '.pl' extension, or
          2.b. mentions 'perl' in first line
      """
      if not os.path.isfile(path):
          #  I prefer string interpolation operator over format()
          raise NotImplementedError('"%s" is not a file' % path)
  
      stem, ext = os.path.splitext(path)
      if ext == '.pl':
          return
      with open(path) as stream:
          if 'perl' in stream.readline():
              return
      raise NotImplementedError('%s is not a perl script' % path)
  
  
  def which_ack():
      """Find the system 'ack' with which
  
      Should be a perl script
      """
      ack = os.environ.get('ACK') or 'ack'
      if not ack or not os.path.isfile(ack):
          status, output = commands.getstatusoutput('which ack')
          if status != os.EX_OK:
              status, output = commands.getstatusoutput('PATH=/usr/local/bin:/usr/bin:/bin which ack')
              if status != os.EX_OK:
                  raise NotImplementedError('"which ack" failed: "%s"' % output)
          ack = output
      assert_perl_script(ack)
      return ack
  
  def main(args):
      """Run this script as a program"""
      if '-U' in sys.argv:
          import pudb
          pudb.set_trace()
      words = [which_ack()]
      for word in args:
          if re.match('-[a-uw-z]*[vV][a-uw-z]*', word):
              words[0] = 'vack'
              words.append(word)
          else:
              if re.search('[.(]', word):
                  if ' $' in word:
                      words.append("'%s'" % word)
                  else:
                      words.append('"%s"' % word)
              else:
                  words.append(word)
      script = os.path.join(os.path.dirname(__file__), 'ack2vim.sh')
      words[0:0] = ('.', script, ';')
      print ' '.join(words)
  
  if __name__ == '__main__':
      sys.exit(main(sys.argv[1:]))
  
subject: Use known PATH to find which