Need help with a regex

Hi I'm trying to right a r开发者_StackOverflow中文版egular expression that will take a string and ensure it starts with an 'R' and is followed by 4 numeric digits then anything

eg. RXXXX.................

Can anybody help me with this? This is for ASP.NET

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You want it to be at the beginning of the line, not anywhere. Also, for efficiency, you dont want the .+ or .* at the end because that will match unnecessary characters. So the following regex is what you really want:

^R\d{4}

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This should do it...

^R\d{4}.*$

• \d{4} matches 4 digits
• .* is simply a way to match any character 0 or more times
• the beginning ^ and end $ anchors ensure that nothing precedes or follows

As Vincent suggested, for your specific task it could even be simplified to this...

^R\d{4}

Because as you stated, it doesn't really matter what follows.

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/^R\d{4}.*/ and set the case insensitive option unless you only want capital R's

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^R\d{4}.*

• The caret ^ matches the position before the first character in the string.
• \d matches any numeric character (it's the same as [0-9])
• {4} indicates that there must be exactly 4 numbers, and
• .* matches 0 or more other characters

To use:

    string input = "R0012 etc..";

    Match match = Regex.Match(input, @"^R\d{4}.*", RexOptions.IgnoreCase);

    if (match.Success)
    {
       // Success!
    }

Note the use of RexOptions.IgnoreCase to ignore the case of the letter R (so it'll match strings which start with r. Leave this out if you don't want to undertake a case insensitive match.