Regular expression: find range except for one letter or a range

Question

How can I use the negation within square brackets as an exception, to find e. g. everything between a-z except for the the range from m-o? [a-z^m-o]?

By the way: it's not for the sake of this example that I ask, but to be able to exclude ranges within ranges, or even single letters within ranges. I am pretty much aware that in this example it can be calculated.

I use the Zend engine (PHP).

Answer 1

You should be able calculate the difference yourself.

[a-lp-z]

If the regex engine supports lookahead assertion, you could use

(?![m-o])[a-z]

but this would probably be less efficient.

Answer 2

In addition to what Kenny mentions:

1. The JDK (at least) supports this syntax:

   [a-z&&[^m-o]]

2. A couple of engines (including the .NET framework) support this:

   [a-z-[m-o]]