List lines matching the interfaces in a Cisco configuration file

list_interfaces.py

import sys
import re


def list_interfaces(input_file):
  with open(input_file) as fp:
    lines = fp.read().splitlines()

  for l in lines:
    match = re.match(r'^Interface (.*)$', l)
    if match:
      yield match.group(0)


if __name__ == "__main__":
  input_file = sys.argv[1]
  interfaces = list_interfaces(input_file)
  print('\n'.join(interfaces))