Regex to match positive or negative number or empty string, but not '-' alone

Question

I want to validate numbers in an input in Javascript.

The input should accept:

• empty input ''
• positive number '123'
• negative number '-123'

I have used this regex:

^(-?)[\d]*$

It works well, but it also accepts only the minus character alone '-' . I want to exclude this possibility. I could of course replace * with +, but that would exclude the empty string.

How can I do it so that a - must be followed by at least one number, but a completely empty string is still OK?

Answer 1

You may make the digits obligatory and enclose the whole number matching part with an optional group:

/^(?:-?\d+)?$/

See the regex demo

Details

• ^ - start of the string
• (?:-?\d+)? - an optional non-capturing group matching 1 or 0 occurrences of:
  • -? - an optional -
  • \d+ - 1 or more digits
• $ - end of string.