input: Write a function to search for any matches of a user's input string in a given list of strings using regular expressions. The function should return "String matches" if a match is found and "String doesn't match" otherwise.
  
  assert str_match("Please enter your string: First")=="String matches"
  assert str_match("Please enter your string: Second")=="String matches"
  assert str_match("Please enter your string: Third")=="String matches"
  assert str_match("Please enter your string: Fourth")=="String doesn't match"
  assert str_match("Please enter your string: T")=="String doesn't match"
output: import re
  
  def str_match(user_input):
      pattern = r"First|Second|Third"
      if re.search(pattern, user_input):
          return "String matches"
      else:
          return "String doesn't match"