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 el

Answer 1

To match a number or empty string '' i.e the user has not entered any input do this

(^[0-9]+$|^$)

To match a number, an empty string, or a white space character

(^[0-9]+$|^$|^\s$)

Test this on regex101