input: Write a function to match all numeric strings using regular expression. The function should take a string as input and return True if the string is a valid numeric string and False otherwise.
  import re
  
  def match_numeric_string(string):
      pattern = '^[0-9]+$'
      result = re.match(pattern, string)
      return bool(result)
  
  assert match_numeric_string('123456789') == True
  assert match_numeric_string('abc123') == False
  assert match_numeric_string('1234a56789') == False
  assert match_numeric_string('') == False
  assert match_numeric_string('9876543210') == True
output: 
  def match_numeric_string(string):
      pattern = '^[0-9]+$'
      result = re.match(pattern, string)
      return bool(result)
  