input: Write a python function to split a string based on a pattern using regular expressions.
  assert split_string("102030-abc-5060", r'-\w+-') == ['102030', '5060']
  assert split_string("123-xyz-456-abc-789", r'-\w+-') == ['123', '456', '789']
  assert split_string("apple-banana-orange", r'-\w+-') == ['apple', 'orange']
output: def split_string(s, pattern):
      import re
      return re.split(pattern, s)