old_contents: import re
  
  patterns = [
      r'WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!',
      r'WARNING: POSSIBLE DNS SPOOFING DETECTED!',
      r"Warning: the \S+ host key for '([^']+)' differs from the key for the IP address '([^']+)'",
  ]
  offending_pattern = re.compile(
      r'(?:Offending (?:key for IP|\S+ key)|Matching host key) in ([^:]+):(\d+)',
      re.MULTILINE)
  
  commands = ['ssh', 'scp']
  
  
  def match(command, settings):
      if not command.script:
          return False
      if not command.script.split()[0] in commands:
          return False
      if not any([re.findall(pattern, command.stderr) for pattern in patterns]):
          return False
      return True
  
  
  def get_new_command(command, settings):
      return command.script
  
  
  def side_effect(old_cmd, command, settings):
      offending = offending_pattern.findall(old_cmd.stderr)
      for filepath, lineno in offending:
          with open(filepath, 'r') as fh:
              lines = fh.readlines()
              del lines[int(lineno) - 1]
          with open(filepath, 'w') as fh:
              fh.writelines(lines)
  
new_contents: import re
  
  
  def match(command, settings):
      if not command.script:
          return False
      if not command.script.startswith(('ssh', 'scp')):
          return False
  
      patterns = (
          r'WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!',
          r'WARNING: POSSIBLE DNS SPOOFING DETECTED!',
          r"Warning: the \S+ host key for '([^']+)' differs from the key for the IP address '([^']+)'",
      )
  
      return any(re.findall(pattern, command.stderr) for pattern in patterns)
  
  
  def get_new_command(command, settings):
      return command.script
  
  
  def side_effect(old_cmd, command, settings):
      offending_pattern = re.compile(
          r'(?:Offending (?:key for IP|\S+ key)|Matching host key) in ([^:]+):(\d+)',
          re.MULTILINE)
      offending = offending_pattern.findall(old_cmd.stderr)
      for filepath, lineno in offending:
          with open(filepath, 'r') as fh:
              lines = fh.readlines()
              del lines[int(lineno) - 1]
          with open(filepath, 'w') as fh:
              fh.writelines(lines)
  
subject: Improve the `ssh_known_hosts` rule import time