regex allow only numbers or empty string

Question

Can someone help me create this regex. I need it to check to see if the string is either entirely whitespace(empty) or if it only contains positive whole numbers. If anything else it fails. This is what I have so far.

/^\s*|[0-9][0-9]*/

Answer 1

You're looking for:

/^(\s*|\d+)$/

If you want a positive number without leading zeros, use [1-9][0-9]*

If you don't care about whitespaces around the number, you can also try:

/^\s*\d*\s*$/

Note that you don't want to allow partial matching, for example 123abc, so you need the start and end anchors: ^...$.
Your regex has a common mistake: ^\s*|\d+$, for example, does not enforce a whole match, as is it the same as (^\s*)|(\d+$), reading, Spaces at the start, or digits at the end.

Answer 2

You can try it-

/^\d*$/

To match with white space-

/^[\s\d\s]*$/

Answer 3

Kobi has a good answer but technically you don't have to capture it (unless you're going to do something the output)

/^[\s\d]+$/

Or if you don't care if the string is completely empty (i.e. "")

/^[\s\d]*$/

To clarify I understood the original question to mean whitespace in the string should be ignored.