\d does not validate numbers


points us to this Perl FAQ:


Unfortunately, the regular expression part of the above FAQ page is wrong. \d doesn't validate numbers, unless you have already verified that your input contains only ASCII characters.

What \d does is to validate whether a number is regarded as a numeral in Unicode. For example, \d will happily match things like U+07C2: '߂' NKO DIGIT TWO, or 096F: '९' DEVANAGARI DIGIT NINE, and 360 other characters which are not valid as numerals. If you need to use a regular expression to validate whether something is a number, use [0-9] to match digits, not \d.

The reason I'm aware of these defects in the use of \d for validating numbers is because of having used it to validate user input at the following web pages:


Before I removed \d everywhere a few years ago, it was not uncommon to unravel bugs resulting from people typing in Devangari or other non-ASCII numerals which had been validated using \d.

(This post was edited on 4 December 2018 to remove links to some old pages which are now gone from my web site.)


That’s what /a is for.

Note that /a requires Perl 5.13.10 or higher.

Then [:digit:] is /d and also not [0-9]

I'm using [0-9].

\d contains Unicode number.

DEVANAGARI DIGIT NINE, for example, is used by millions of people millions, perhaps billions, of times a day as an essential component of their numbers. I don't know if you are being careless with your terminology, or wrongly arrogant about the place in the universe of [0-9].

Unicode::UCD::num(), since Perl 5.14, can be used to make sure that a string of digits are all from the same script, so are not spoofing attempts, returning the numeric value the string represents, or undef if it is illegal.

Leave a comment

About Ben Bullock

user-pic Perl user since about 2006, I have also released some CPAN modules.