Regex to accept only numbers

Solution
Regular expression - (^[0][1-9]+)|([1-9]\d*)
Test online - Here[^].

Examples
12345678 - 12345678
0 - Not mached.
01567 - 01567
0000 - Not matched.
bbbb - Not matched.
1 9999 - Space character is not matched, instead it is taken as two different numbers as "1", "9999".

Note
-> All the test strings are written in left box.
-> All the matched results are written in right box.
-> You can also check, which group got executed for the matched string (in box "Match groups" below the right "Match result" box),
where Group-1 is (^[0][1-9]+) and Group-2 is ([1-9]\d*).

For example - 12345678 is matched by Group-2 and not by Group-1.

Thanks...