Clever Geek Handbook

Is there a regular expression that will never match any string?

Ask the question in two parts:

  • Is there any theoretical regex that will never match any string (using a general syntax without any of the fancy stuff provided by modern regex)?
  • Is there an easy way to use the C # Regex syntax to create a regex that will never match any string (all the fancy stuff included this time)?

NOTE. I am not referencing empty string matching (that would be simple, simple ""

).

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3 answers


Just like you can match any characters to [\s\S]

, you cannot match characters to [^\s\S]

(or [^\w\W]

, etc.).



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Without multiline mode, the end usually doesn't appear before the start:

$.^

Or simpler, again without multi-line mode:

$.


With search engines, you can do all sorts of conflicting things:

(?=a)(?=b)

This forces the hero to be two different things at once, which, of course, is impossible.

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You can use conflicting lookbehinds like

\w(?<!\w)

Here \w

will match any character of the word, and lookbehind (?<!\w)

will make sure the last character is not a word.

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