Matching Hex characters in a Regex

I've noticed a common problem with regular expressions and Hex Characters, so I thought I'd blog about it. The most common way to regex a UUID, or SHA1 or some other hex encoded binary value is this (and I've seen this in Perl libraries and StackOverflow answers).

[a-f0-9] or [A-F0-9]

Neither of these are correct as Hex is case insensitive and both of these regex's are. Hex is most commonly lowercase (unless you're Data::UUID), but that's an aesthetic, not a requirement. The best way to match Hex is using a POSIX character class.

[[:xdigit:]] or \x

which matches this in a more readable manner, and intent driven manner

[A-Fa-f0-9]

as a side note it's this in a regex string in Java

"\\p{XDigit}"

empty() function for postgresql in sql

In PostgreSQL the ASCII NULL or empty string \0 is seen as NOT NULL. This is because postgres developers consider any characters data. I know there are better discussions on it but I can't find them right now. Unfortunately the programming language you are using probably doesn't see it the same way. There's a good chance that initialized variables are set to \0 and so when you try to insert from your language to a NOT NULL field with variables that are seen as undefined in your language, postgres accepts it, and now you have fields that you probably consider to have no data but are NOT NULL.

My function possibly would be better called empty_or_whitespace but in my mind any text field that contains only whitespace is empty, and I'd rather have 1 function and 1 regex deal with both than have 2 functions have to be called on every insert/update.

Here is the gist

It returns true if an empty string is found. It really requires a knowledge of SQL, PostgreSQL's CREATE FUNCTION, and Regular Expressions, to understand. Thanks to the wonderfully helpful PostgreSQL community with perfecting it.

In order to use it to keep ASCII NULLS and fields that someone has just entered whitespace into you need to add it to your table as a constraint.

Here's an example create table gist using it.

remember it returns true on null's and whitespace so you have to say NOT emtpy( field ).