regex - Regular Expression Opposite

Question

Is it possible to write a regex that returns the converse of a desired result? Regexes are usually inclusive - finding matches. I want to be able to transform a regex into its opposite - asserting that there are no matches. Is this possible? If so, how?

http://zijab.blogspot.com/2008/09/finding-opposite-of-regular-expression.html states that you should bracket your regex with

/^((?!^ MYREGEX ).)*$/

, but this doesn't seem to work. If I have regex

/[a|b]./

, the string "abc" returns false with both my regex and the converse suggested by zijab,

/^((?!^[a|b].).)*$/

. Is it possible to write a regex's converse, or am I thinking incorrectly?

Answer 1

Couldn't you just check to see if there are no matches? I don't know what language you are using, but how about this pseudocode?

if (!'Some String'.match(someRegularExpression))
    // do something...

If you can only change the regex, then the one you got from your link should work:

/^((?!REGULAR_EXPRESSION_HERE).)*$/