Validating input with Regex

Question

I need to validate input to my application. The input is a formatted string that may contain parts of a Date, e.g.:

{0:yy}{0:MM}{0:dd}_{0:hh}{0:mm}{0:ss}-SOME OTHER TEXT
sometext{0:yyyy}{0:MM}{0:dd}mORETEXT

The input doesn't have to contain those parts of a date, but if it does, I need them to be valid format items that can be used by String.Format() method. I believe I should validate using Regular Expressions, but I am not good at it.

Could you please help?

So you're trying to parse dates out of an arbitrary string? Or are you doing assertive validation? — bluevector
– bluevector, Commented Jun 21, 2012 at 14:17
I am not sure what assertive validation is. I store these strings in the database, and use them in my C# code like this: FileName = String.Format(dr["FileNameTemplate"].ToString(), DateTime.UtcNow) — David Shochet
– David Shochet, Commented Jun 21, 2012 at 14:32
So I don't want the user to enter invalid format item like "SomeText{garbage}moreText{moregarbage}theend" — David Shochet
– David Shochet, Commented Jun 21, 2012 at 14:37
That sounds like parsing, then. By "assertive validation" I meant putting on the brakes and telling the user "no, that's not valid - fix it". — bluevector
– bluevector, Commented Jun 21, 2012 at 14:39
So if the string contains single curly brace, there must be a closing brace, and between them there must be "0:" plus a valid part of a DateTime. I mean valid to be used as a format item in C#'s String.Format() method. — David Shochet
– David Shochet, Commented Jun 21, 2012 at 14:40

bluevector · Accepted Answer · 2012-06-21 20:48:55Z

1

Given our back-and-forth via comments, I think the what you are looking for is:

        Regex curlyThings = new Regex(@"\{0:.*?\}");
        Regex kosherCurlyThings = new Regex(@"\{0:(yy|yyyy|MM|dd|hh|mm|ss)\}");

        MatchCollection matchCollection = curlyThings.Matches("CG{0:yyyy}-{0:MM}-{0:dd}asdf{0:GARBAGE}.csv");
        foreach(Match match in matchCollection)
        {
            if(!kosherCurlyThings.IsMatch(match.Value))
            {
                Console.WriteLine("{0} isn't kosher!", match.Value);
            }                
        }

edited Jun 21, 2012 at 20:48

answered Jun 21, 2012 at 14:43

bluevector

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16 Comments

m0skit0 Over a year ago

You probably want to escape { and } characters since they're special characters in regexes.

David Shochet Over a year ago

@jonnyGold Hmmm... Something goes wrong. I tried to test this with the following code:

David Shochet Over a year ago

var r = new Regex(@".*?(\{0:yy(yy)?\}\{0:MM\}\{0:dd\}(_\{0:hh\}\{0:mm\}\{0:ss\}))?.*?"); if (!r.IsMatch("CG{0:yyyGARBAGEy}-{0:MM}-{0:dd}.csv")) { var blah = "The format is invalid!"; }

David Shochet Over a year ago

But it my bad string was found valid... Am I doing something wrong?

bluevector Over a year ago

I just thought of a better answer that should work... take a look.

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