mobilityiop.blogg.se - Regular expression not to match

via syntax) that carries out the subtraction - after matching what needs to be subtracted. This is how every tool that uses regexps works (e.g., grep): they offer a separate option (e.g. IOW, do not try to make the regexp do the excluding (it cannot) do the excluding after using a regexp to match what you want to exclude. The answer is to use a regexp to match what you do not want, and then subtract that from the initial domain. What is the real use case - what are you really trying to do?Īs Tomalak indicated, (a) this is not what regexps do (b) see the other post he linked to, for a good explanation, including what to do about your problem. Unless you have a function that generates such regexps (as Gumbo shows), composing them would be a real pain. Hard to believe that the accepted answer (from Gumbo) was actually accepted! Unless it was accepted because it indicated that you cannot do what you want. The pattern of this regular expression is to allow any character that is not the first character of the words or only prefixes of the words but not the whole words. This would also exclude words like nil ( does not match), bob ( does not match) or cat ( does not match).īut it is possible to build a regular expression with basic syntax that does match strings that neither contain not nor this: ^(|n($||o($|))|t($||h($||i($|))))*$

rewrite the expression so it can match: see a similar question I asked earlierįirst of all: is not a solution.

use negative look-ahead, if supported by your regex engine and feasible in the situation.

match (not|this) and exclude any matches with the help of the environment you are in (negate match results).

Three ways can lead out of this situation:

Your try is 100% equivalent to, as far as the regex engine is concerned. They support single characters (and, for convenience, character ranges). That pattern can be used to match, search, substring, or split text. It is input as a text string itself, and will compile into a mini program built specifically to identify that pattern. Character classes do not support grouping in any form or shape. A regular expression matches a broad or specific text pattern, and is strictly read left-to-right. Regular expressions are designed to match things, and this is all they can do.įirst off: does not designate an "excludes group", it designates a negated character class.