c# Regex, how can I escape [[ and ]]

Question

I'm trying to instantiate a new Regex class with the regular expression

var reg = new Regex("[[" + token.Key + "]]");

But I'm getting the following error

System.ArgumentException: 'parsing "[[Impact]]" - [x-y] range in reverse order.'

How can I instantiate the new class with the double square brackets in the regular expression?

First of all, interestingly I don't get such an exception. On the other hand, what you are trying to achieve? you want the regex to match [[ and ]] as literals? — ZorgoZ, Jul 26 '18 at 06:29
Yes, it doesn't work. I'll try `\\[\\[` and see what happens — Train, Jul 26 '18 at 06:29
@ZorgoZ According to my duplicate down vote which isn't really a duplicate, but very informative none the less, it might be a different flavor of regex you're using. — Train, Jul 26 '18 at 15:53
@OrthoHomeDefense I did not know that .net has different flavors of RegEx. I was using the latest one in LinqPad. — ZorgoZ, Jul 26 '18 at 16:41

score 4 · Answer 1 · answered Jul 26 '18 at 06:40

4

You could use built-in functions to escape things:

var re = Regex.Escape("[[") + token.Key + Regex.Escape("]]");
var reg = new Regex(re);

But you may also want to escape the token.Key?

Or just use a string.Contains(...), if you don't want the special features of regex.

answered Jul 26 '18 at 06:40

Hans Keﬆing

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apparently, the set of closing brackets do not need to be escaped. I tried it on regexpal: https://www.regexpal.com/?fam=104272 – Manuel Hoffmann Jul 26 '18 at 06:44
@ManuelHoffmann Yes that is true, inspecting the escaped string shows that also. But when they are not known literals, you might want to play it safe. – Hans Keﬆing Jul 26 '18 at 06:47
Of course that is absolutely correct. I just mentioned it because in case anyone didn't know. – Manuel Hoffmann Jul 26 '18 at 06:50

score 3 · Accepted Answer · answered Jul 26 '18 at 06:41

You need to escape the characters "[" and "]" for the regular expression, and if you are using "\" to escape the brackets, then you need to escape those in your C# string as well.

That means it can be either:

"\\[\\[" + key + "]]"

or

@"\[\[" + key + "]]"

or

Regex.Escape("[[") + key + "]]"

You don't need to escape the latter "]" because Regex recognizes them as normal characters if you don't have an unescaped "[" before them. I tried it on Regexpal (a regex testing website) and other answers suggest it as well.

Thanks, everyone had good answers but this one gives an explanation. — Train, Jul 26 '18 at 06:47

ZorgoZ · Answer 3 · 2018-07-26T06:40:45.153

2

This one works:

var reg = new Regex(@"\[\[" + token.Key + @"]]");

(Note: the second @ is not actually needed)

Update: This is even better:

var reg = new Regex($@"\[\[{token.Key}]]");

edited Jul 26 '18 at 06:40

answered Jul 26 '18 at 06:36

ZorgoZ

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what is that extension called? – slow Jul 26 '18 at 06:36
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This screenshot is a LinqPad snippet. `.Dump` is part of it, but this is something similar: https://github.com/victorjspinto/101-Linq-Samples/blob/master/LINQ%20-%20Quantifiers/C%23/Quantifiers/ObjectDumper.cs – ZorgoZ Jul 26 '18 at 06:39
@vc74 yes, I have already noted that, as you can see – ZorgoZ Jul 26 '18 at 06:45

score 1 · Answer 4 · answered Jul 26 '18 at 06:29

1

Just escape every bracket with a bracket like is shown below:

var reg = new Regex("[[[["+ token.Key +"]]]]");

answered Jul 26 '18 at 06:29

Samvel Petrosov

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score 1 · Answer 5 · answered Jul 26 '18 at 06:32

1

Try

var reg = new Regex("[[][[]" + token.Key + "[]][]]");

it will match, for example [[Impact]] if token.Key equals "Impact".

answered Jul 26 '18 at 06:32

Michał Turczyn

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c# Regex, how can I escape [[ and ]]

5 Answers5