input: Write a function to match all numeric strings using a regular expression. The function should take a string as input and return True if the string is a valid numeric string, and False otherwise. If the input string is empty, the function should return False.
  
  import re
  
  def is_numeric_string(string):
      if not string:
          return False
      pattern = '^[0-9]+$'
      result = re.match(pattern, string)
      return bool(result)
  
  assert is_numeric_string('123456789')==True
  assert is_numeric_string('abcdef')==False
  assert is_numeric_string('123abc456')==False
  assert is_numeric_string('')==False
  assert is_numeric_string('0')==True
output: 
  def is_numeric_string(string):
      if not string:
          return False
      pattern = '^[0-9]+$'
      result = re.match(pattern, string)
      return bool(result)
  