Regular expression to match anything that isn't the string "ABCD"

Question

How do I write a Javascript regular expression that matches everything except a given string ("ABCD")?

Something like /[^ABCD]/ except I don't want to match everything that isn't the letter A, B, C or D. I want to match everything that isn't the string "ABCD".

Basically I want this to happen:

var myStr = "ABCA ABCB ABCD BCD ABC"
myStr.replace(/!(ABCD)/g,'') // returns ABCD

Your problem can probably be solved better without regex. What are you actually trying to do? — Kendall Frey, Aug 09 '12 at 22:46
Trying to strip everything from some text that isn't a particular string. — brentonstrine, Aug 09 '12 at 22:47
Query: if `myStr = "ABCA ABCB ABCD BCD ABC ABCD"`, should `ABCDABCD` be returned? — Paul D. Waite, Aug 09 '12 at 22:50
@godspeedlee, I think I want to do the exact opposite of that. — brentonstrine, Aug 09 '12 at 22:51
@PaulD.Waite I'd accept an answer that would return just ABCD (once) though, as it works for my purposes, but I just assumed that there was a way to negate a string in regex. — brentonstrine, Aug 09 '12 at 22:57
http://stackoverflow.com/questions/406230/regular-expression-to-match-string-not-containing-a-word — dqhendricks, Aug 09 '12 at 22:58
Sorry, I misunderstood your question. I guess you want to remove non ABCD words from the string, right? — godspeedlee, Aug 09 '12 at 23:39

kapa · Answer 1 · 2012-08-09T22:53:56.427

5

You can simply check for ABCD, check how many of it exists in the string, then construct a new string from it like this (you can use space as a separator if it fits your case better):

var res = myStr.match(/ABCD/g);
var str = res ? res.join('') : '';

The ternary is there because match() will return null if it finds nothing - which does not have a join() method.

edited Aug 09 '12 at 22:53

answered Aug 09 '12 at 22:48

kapa

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Good answer, but I was really looking for a way to do this with regex. – brentonstrine Aug 09 '12 at 23:11
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@brentonstrine Well, I used regex :) – kapa Aug 09 '12 at 23:13
I feel like you didn't answer the spirit of my question about regex, but I did end up using `.match()` in my actual code, so thanks. +1. – brentonstrine Aug 10 '12 at 04:39
@brentonstrine IMO a classic regex is not the best tool to solve this problem, that's why I tried to provide an alternative. There are a thousand other ways of course, even not using a regex at all. Please accept an answer if you think it is good enough, so everyone can see the problem is solved. Of course it's no problem at all if you accept Alan's answer, it is a good one. – kapa Aug 10 '12 at 07:55
Whoops, I thought I had accepted his. I wish I could accept both Alans and yours. – brentonstrine Aug 10 '12 at 15:37

Alan Moore · Accepted Answer · 2012-08-10T00:24:14.443

Okay, I had misinterpreted the question. It seems you want to test for the presence of ABCD, and if you find it, replace the whole string with just that: ABCD. This will do that:

s = s.replace(/.*(ABCD).*/, '$1');

But it will leave the string unchanged if there's no ABCD in it. If you want to delete the string in that case, you have to make the capture optional. But then you have to alter the first part of the regex to make it "sneak up" on the capture:

s = s.replace(/^(?:(?!ABCD).)*((?:ABCD)?).*$/, '$1');

That forces it to try to capture ABCD at every position. (It also slows things down massively--not an issue in this case, but something to keep in mind if you use this technique on large inputs.)

So a pure-regex solution does exist, but I like @bažmegakapa's solution better. :D

original answer:

/^(?!ABCD$).*/

Note that this will also match an empty string. If you have any positive requirements, you can change the .* to whatever you need. For example, to match one or more uppercase ASCII letters but not the exact string ABCD, you can use:

/^(?!ABCD$)[A-Z]+$/

I may be doing something wrong, but that seems to also match `ABCD`. http://www.myregextester.com/?r=c725cba3 — brentonstrine, Aug 09 '12 at 23:08
True, @ bažmegakapa's solution is better, and ultimately in my code, using `.match()` ended up being even simpler than his answer for my purposes, but I could have come up with a hundred other ways to address my initial issue. This question was about regular expressions! I wish I could split the "answer" but I did upvote both. — brentonstrine, Aug 10 '12 at 04:38

alinsoar · Answer 3 · 2012-08-10T11:24:34.617

0

This is a direct expansion of the negation , without using a negation operator:

/^\([^a]\|a[^b]\|ab[^c]\|abc[^d]\)*$\|^a$\|^ab$\|^abc$/

When you call a negation operator into some language, it transform the expression you want to negate into something like the upper form .

Here is how I tested it:

@ThinkPad-T420:~$ E='/^\([^a]\|a[^b]\|ab[^c]\|abc[^d]\)*$\|^a$\|^ab$\|^abc$/ p;d'
@ThinkPad-T420:~$ echo abc | sed "$E"
abc
@ThinkPad-T420:~$ echo abcd | sed "$E"
@ThinkPad-T420:~$ echo abcde | sed "$E"
@ThinkPad-T420:~$ echo axbcde | sed "$E"
axbcde
@ThinkPad-T420:~$ echo xxabcde | sed "$E"
@ThinkPad-T420:~$

edited Aug 10 '12 at 11:24

answered Aug 09 '12 at 23:25

alinsoar

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That seems not to match anything at all. http://www.myregextester.com/?r=3ece4a12 – brentonstrine Aug 10 '12 at 00:25
I tested it with sed. If you test it with something else, then perhaps you need to insert some backslashed or some minor change. – alinsoar Aug 10 '12 at 11:14
did you manage, finally, to adapt it to your need ? I tested it in shell script, not in javascript. – alinsoar Aug 11 '12 at 09:34

godspeedlee · Answer 4 · 2012-08-09T23:46:00.203

0

try with this:

var myStr = "ABCA ABCB ABCD BCD ABC";
var foo = myStr.replace(/\b(?!ABCD\b)\w+\b/g,'').trim(); // returns ABCD
document.write(foo);

output: ABCD

or:

var myStr = "ABCA ABCB ABCD BCD ABCD ABC";
var foo = myStr.replace(/\b(?!ABCD\b)\w+\b/g,'').replace(/\s/g, '');
document.write(foo);

output: ABCDABCD

edited Aug 09 '12 at 23:46

answered Aug 09 '12 at 23:30

godspeedlee

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Regular expression to match anything that isn't the string "ABCD"

4 Answers4