As no one has given you an answer: Ask Ubuntu is all about providing support for [Ubuntu and its official derivatives](https://wiki.ubuntu.com/UbuntuFlavors) by an army of volunteers (no we don't get paid for doing this) so everyone answers the questions they like and know something about.

There are a few things [we do](https://askubuntu.com/help/on-topic) and [don't do](https://askubuntu.com/help/dont-ask), but I suspect you never received an answer to your [original question](https://askubuntu.com/questions/751734/why-dont-posix-regular-expression-character-classes-work-in-mawk) because *no one uses `mawk` any more because there are [better alternatives](http://lmgtfy.com/?q=alternative+mawk)*.

And why Canonical (the company behind Ubuntu) still ships `mawk`?  We can only guess, and that is off-opic here...  **;-)**

So what can you do if `mawk` is that important to you?

Well, fix the bug yourself, hire a developer to do it for you and post the fix upstream, contact the developer, ... But definitely, [go here](http://invisible-island.net/mawk/mawk.html)!

# ;-)