Trouble creating a Regex expression

Question

I'm trying to create a regex expression what will accept a certain format of command. The pattern is as follows:

Can start with a $ and have two following value 0-9,A-F,a-f (ie: $00 - $FF) or Can be any value except for "&<>'/"

*if the value start with $ the next two values after need to be a valid hex value from 00-ff

So far I have this

Regex correctValue = new Regex("($[0-9a-fA-F][0-9a-fA-F])");

Any help will be greatly appreciated!

I don't understand this part of your question: Can be any value except for "&<>'/". Do you mean it should match any single character that's not in that list? — Pete Schlette
– Pete Schlette, Commented Aug 1, 2012 at 1:02

horgh · Accepted Answer · 2012-08-01 02:08:19Z

3

You just need to add "\" symbol before your "$" and it works:

        string input = "$00";

        Match m = Regex.Match(input, @"^\$[0-9a-fA-F][0-9a-fA-F]$");
        if (m.Success)
        {
            foreach (Group g in m.Groups)
                Console.WriteLine(g.Value);
        }
        else
            Console.WriteLine("Didn't match");

answered Aug 1, 2012 at 2:08

horgh

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1 Comment

horgh Over a year ago

Well, I also added ^ and $ to mark the beginning and the ending of the regex

Ken Pespisa · Accepted Answer · 2012-08-01 01:07:30Z

2

If I'm following you correctly, the net result you're looking for is any value that is not in the list "&<>'/", since any combination of $ and two alphanumeric characters would also not be in that list. Thus you could make your expression:

Regex correctValue = new Regex("[^&<>'/]");

Update: But just in case you do need to know how to properly match the $00 - $FF, this would do the trick:

Regex correctValue = new Regex("\$[0-9A-Fa-f]{2}");

answered Aug 1, 2012 at 1:07

Ken Pespisa

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Comments

Ria · Accepted Answer · 2012-08-01 04:25:43Z

2

In Regular Expression $ use for Anchor assertion, and means:

The match must occur at the end of the string or before \n at the end of the line or string.

try using [$] (Character Class for single character) or \$ (Character Escape) instead.

answered Aug 1, 2012 at 4:25

Ria

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