Regex to capture characters not specified in pattern

Question

I have a string "this [is] not req!red"

i am trying to create a regex which will pick "characters" not specified in the list

[-a-zA-Z.,-()=\s\+:?!*\;><0-9]

any suggestions how to achieve this?

Language is C#

Have you googled "regex not"? It's that simple. `[abc]` is "the character a, b or c". `[^abc]` is "any character that isn't a, b or c". `[^abc]+` is "any character that isn't a, b or c matched 1 to infinity times". — h2ooooooo, Apr 25 '14 at 13:18
depends on your language, `^` at the beginning generally negates a character class and you can use captures to get them: `([^-a-zA-Z.,-()=\s+:?!*\;><0-9]). — perreal, Apr 25 '14 at 13:20
okay your regex changed to `[^-a-zA-Z.,\-()=\s\+:?!*\;><0-9]` selects only the square brackets so what is your problem? — aelor, Apr 25 '14 at 13:29
Is your goal to end up with `this is not reqred`? To filter out all unwanted characters? Every letter is *unwanted*? — aliteralmind, Apr 25 '14 at 13:32
I am using C#, basically i want to replace all characters which don't match this particular pattern. — Usman Masood, Apr 25 '14 at 14:10

score 2 · Accepted Answer · edited May 23 '17 at 10:26

2

Your regex is a positive character class that matches each legal character specified in it:

[-a-zA-Z.,\-()=\s+:?!*\;><0-9]

Regular expression visualization

Debuggex Demo

The characters you don't want aren't matched. To switch this around, to match only the characters you want, make it a negative character class, by adding the ^ as its first character:

[^-a-zA-Z.,\-()=\s+:?!*\;><0-9]

Regular expression visualization

Debuggex Demo

To capture the matches, put the entire regex into a capturing group:

([-a-zA-Z.,\-()=\s+:?!*\;><0-9])

or

([^-a-zA-Z.,\-()=\s+:?!*\;><0-9])

Then iterate through the matches in your language of choice. Each character is in capture group one.

I'm uncertain of your goal. More information would help us give you better answers.

Please consider bookmarking the Stack Overflow Regular Expressions FAQ for future reference.

edited May 23 '17 at 10:26

Community

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answered Apr 25 '14 at 13:34

aliteralmind

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I want to replace all those characters which are not in my Regex allowed list. – Usman Masood Apr 25 '14 at 14:12
@UsmanMasood So you use the regex as `string output = Regex.Replace(input, @"[^a-zA-Z.,\-()=\s+:?!*\;><0-9]", ".");` where "." is the replacement symbol. – Ulugbek Umirov Apr 25 '14 at 14:14
I don't know C#, but as a generic regex replacement, it looks fine. Tell me what happens. – aliteralmind Apr 25 '14 at 14:25

score 1 · Answer 2 · answered Apr 25 '14 at 13:30

I think you need this :

[^-a-zA-Z.,\-()=\s\+:?!*\;><0-9]

the ^ will negate every character present in the list .

demo here : http://regex101.com/r/vX0oQ7

so basically in your example, it will not select anything apart from the square brackets .

this [is] not req!red
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Regex to capture characters not specified in pattern

2 Answers2