To search Wikipedia live with regular expressions, use the insource: parameter, followed by your regex search string enclosed in forward slashes, like this: /regular expression/. Here is an example:
insource:/(Abraham|Abe) Lincoln/
insource searches the wikitext version of articles, and so, wikiformatting codes can be included in the search string. If any characters you wish to find are used as special characters within regex, they will need to be "escaped" by preceding each with a backslash. For a cheat sheet on writing regexes, see Wikipedia:AutoWikiBrowser/Regular expression.
For case insensitive searches, include an "i" after the closing forward slash.
To search all of Wikipedia offline using regex, you need to download the Wikipedia database and do the search offline with AutoWikiBrowser's Database Scanner. Activate it from the tools menu in AutoWikiBrowser (AWB). It returns the names of the pages that match your query, which you can have sent directly to AWB's list maker (then you can use AWB to view them all). The Database Scanner has many features, and each query can be easily configured to match, exclude, specify namespaces, ignore redirects, etc. as you see fit.