Regex to validate number between two ranges

The . character has special meaning in a regex, so you need to escape it.

Anyway, let me see if I got the rules straight:

• Decimal point is optional
• If decimal point not given:
  • Between 1 and 5 digits
• If decimal point is present:
  • Between 0 and 5 digits before decimal point
  • Between 1 and 2 digits after decimal point

Since the number of digits depends on the presence of the decimal point, you make the regex have two choices, separated by |.

Choice 1 (no decimal point): [0-9]{1,5}

Choice 2 (decimal point): [0-9]{0,5}\.[0-9]{1,2}

Since you want anchors (^$), you can either put them in both choices, or surround the choice set with parenthesis. To make it non-capturing, use (?:xxx).

Final regex is one of these:

/^[0-9]{1,5}$|^[0-9]{0,5}\.[0-9]{1,2}$/
/^(?:[0-9]{1,5}|[0-9]{0,5}\.[0-9]{1,2})$/

You can see the second one in effect on regex101.

If javascript then below regex would work:

^\d{0,5}(((\.){0})|((\.){1}\d{1,2}))$

All the above mentioned cases are satisfying.

Javascript regex:

/^\d{1,5}(\.\d{1,2})?$/

Javascript demo

The regex ^(?:\d{1,5}(?:\.\d{1,2})?|\.\d{1,2})$ is what I was trying to get.