Regex Examples

Numeric Ranges

Since regular expressions deal with text rather than with numbers, matching a number in a given range takes a little extra care.

You can’t just write [0-255] to match a number between 0 and 255. Though a valid regex, it matches something entirely different. [0-255] is a character class with three elements: the character range 0-2, the character 5 and the character 5 (again). This character class matches a single digit 0, 1, 2 or 5, just like [0125].

The regex [0-9] matches single-digit numbers 0 to 9. [1-9][0-9] matches double-digit numbers 10 to 99.

Floating Point Numbers

As an example, we will try to build a regular expression that can match any floating point number. Our regex should also match integers and floating point numbers where the integer part is not given.

When creating a regular expression, it is more important to consider what it should not match, than what it should.