Question

I need a regular expression that matches UTF-8 letters and digits, the dash sign (-) but doesn’t match underscores (_), I tried these silly attempts without success:

• ([\w-^_])+
• ([\w^_]-?)+
• (\w[^_]-?)+

The \w is shorthand for [A-Za-z0-9_], but it also matches UTF-8 chars if I have the u modifier set.

Can anyone help me out with this one?

Answer 1

Try this:

(?:[\w\-](?<!_))+

It does a simple match on anything that is encoded as a \w (or a dash) and then has a zero-width lookbehind that ensures that the character that was just matched is not a underscore.

Otherwise you could pick this one:

(?:[^_\W]|-)+

which is a more set-based approach (note the uppercase W)

OK, I had a lot of fun with unicode in php’s flavor of PCREs 😀
Peekaboo says there is a simple solution available:

[\p{L}\p{N}\-]+

\p{L} matches anything unicode that qualifies as a Letter (note: not a word character, thus no underscores), while \p{N} matches anything that looks like a number (including roman numerals and more exotic things).
\- is just an escaped dash. Although not strictly necessary, I tend to make it a point to escape dashes in character classes… Note, that there are dozens of different dashes in unicode, thus giving rise to the following version:

[\p{L}\p{N}\p{Pd}]+

Where “Pd” is Punctuation Dash, including, but not limited to our minus-dash-thingy. (Note, again no underscore here).