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There are some pretty cool challenges out there involving regex (Self-matching regex, Regex validating regex)

This may well be impossible, but is there a regex that will ONLY match itself?

NOTE, delimiters must be included:

for example /thing/ must match /thing/ and not thing . The only match possible for your expression must be the expression itself. Many languages allow the implementation of a string in the place of a regular expression. For instance in Go

package main import "fmt" import "regexp" func main() { var foo = regexp.MustCompile("bar") fmt.Println(foo.MatchString("foobar")) }

but for the sake of the challenge, let the expression be delimited (starting symbol, expression, ending symbol ex: /fancypantpattern/ or @[^2048]@ ), if you want to argue quotes as your delimiter, so be it. I think given the apparent difficulty of this problem it won't make much of a difference.

To help you along:

Quick hack I put together for rubular.com (a webpage for ruby regex editing):

var test = document.getElementById("test") ,regex = document.getElementById("regex") ,delimiter="/" ,options = document.getElementById("options") ,delay = function(){test.value = delimiter + regex.value + delimiter + options.value} ,update = function(e){ // without delay value = not updated value window.setTimeout(delay,0); } regex.onkeydown = update; options.onkeydown = update;

Even though this is technically 'code golf' I will be very impressed if anyone can find an answer/ prove it is impossible.

Link is now fixed. Sorry to all

Winning answer thus far: jimmy23013 with 40 characters