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

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

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.

Answer 3

This helped me. It matches empty string and any number you enter.

/^(|\d)+$/

Try here if you want: regex101.com

Answer 4

You can try it-

/^\d*$/

To match with white space-

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

Answer 5

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

Answer 6

^\d+([\.\,][0]{2})?$

I found this worked for me. Allow any whole number, but only a decimal of .00

Pass

• 999 90
• 100
• 100.00
• 101.00
• 1000.00

Fails

• 101.01
• 1000.99

Try it at http://regexpal.com/