calculator program help

I'm trying to make a simple RPN calculator that reads in regular expressions from a file and evaluates them to execute code. Currently I have these regular expressions stored in an array of class objects that have 2 data objects (1. The regex itself and 2. The block of code that should be executed when a match is found). An example of one of the read in regex's is below:
[0-9]+
lambda {|input| $myStack.push(input)}

Now, I get input from the user and compare that string to all the regular expressions in my array. When a match is found, the code is evaluated. So far it is working by entering in input one by one. Code and an example are below.

while input = gets
  for i in 0..$regexArray.length-1
    if ( input =~ Regexp.new($regexArray(i).regex) )
      eval($regexArray(i).code).call(input)
    end
  end
end

Example:
5
4
+
print

will give "9" as it should. However, I want to make it so I can enter input in one line like:
5 4 + print

I've tried matching the input string with the regex with: myMatch = regex.match(input)
but when I enter a string such as "123 456" only the last part ("456") is matched when I need to first match the ("123"). Any help would be appreciated.