RegEx in Ruby: Just one match?

Question

I'm trying to figure out how to check if a string matches a regular expression, but I want to know if the entire string matches just once. Here's my code but it seems absurdly long

def single_match(test_me, regex)
  ret_val = false
  test = regex.match(test_me)
  if (test.length==1 && test[0].length == test_me.length)
      ret_val = true
  end
  return ret_val
end

is there an easier way to do this?

P.S. Here's the method I'm really trying to write, since people always seem to ask why I want the gun these days:

def is_int(test_me)
  return single_match(test_me, /[0-9]*/)
end

Edit Thanks everybody. Here's where I'm really using it, but this regex stuff is always interesting to go through. Thanks for the great and educational answers.

Answer 1

This?

def single_match(str, regex)
  str.match(regex).to_s == str
end

Answer 2

You don't need to do this, your method can be replaced by using the regular expression of /^[0-9]*$/. The ^ tells it match start of a line and $ tells it match end of the line. So it will match: start of line, 0 to any in range of 0 to 9, and finally end of line.

def is_int(test_me)
  test_me =~ /^[0-9]*$/
end

And you don't need the return statements, Ruby implicitly returns the last statement.

Edit:

It probably would be easier and look better to use the to_i instance method of String class.

def is_int(test_me)
  test_me.to_i.to_s == test_me
end

Edit: (did some tests)

Comparing the performance between the two methods shows that .to_i.to_s == way is 5% faster. So it is up to personal preference to which ever looks better and if you want to handle leading zeroes.

Answer 3

To do what you really want should be even simpler

def is_int(test_me)
  test_me.to_i.to_s == test_me
end

Answer 4

To answer your original question, for the sake of people finding this page in a search, "scan" will return an array of matches, so if you want to find out how many times some regexp matches, e.g. how many runs of digits there are, you can do:

mystring.scan(/\d+/).size