Regex to *not* match any characters

Question

I know it is quite some weird goal here but for a quick and dirty fix for one of our system we do need to not filter any input and let the corruption go into the system.

Answer 1

A simple and cheap regex that will never match anything is to match against something that is simply unmatchable, for example: \b\B.

It's simply impossible for this regex to match, since it's a contradiction.

References

• regular-expressions.info\Word Boundaries
  • \B is the negated version of \b. \B matches at every position where \b does not.

Answer 2

Have you tried this simple regex? [^.]*

Answer 3

Another very well supported and fast pattern that would fail to match anything that is guaranteed to be constant time:

$unmatchable pattern $anything goes here etc.

$ of course indicates the end-of-line. No characters could possibly go after $ so no further state transitions could possibly be made. The additional advantage are that your pattern is intuitive, self-descriptive and readable as well!

Answer 4

You want to match nothing at all? Neg lookarounds seems obvious, but can be slow, perhaps ^$ (matches empty string only) as an alternative?