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In my model class, I have a property called ContactNo. I want a regular expression for validation purposes. It should validate that the property starts with "01" and has 11 characters, all numerical.

Steve Konves
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Waheed
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    You do not need a regex for that. Check numeric with `.All(p => Char.IsDigit(p))`, `01` with `.StartsWith("01")` and length with `.Length == 11`. You can even set different error messages with this approach. – Wiktor Stribiżew Aug 12 '16 at 14:26
  • You should checkout this [question](http://stackoverflow.com/questions/123559/a-comprehensive-regex-for-phone-number-validation) and its answers, if true it is on the tangent of your question, it should be helpful to you – Luiso Aug 12 '16 at 14:37

2 Answers2

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The RegEx for the above 

^01[0-9]{9}$

[0-9]{9} because after 01 the remaining length should be 9 numbers You can check the site http://regexr.com/ helps out a lot with RegEx especially if you are a beginner like me.

ZerosAndOnes
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    I doubt it will be working for OP. See [your regex demo](http://regexstorm.net/tester?p=01%5b0-9%5d%7b9%7d&i=015555555550155555555501555555555015555555550155555555501555555555). It does not check the length at all. – Wiktor Stribiżew Aug 12 '16 at 14:39
  • @WiktorStribiżew Thank you for pointing that out, added the anchors to check the exact length. – ZerosAndOnes Aug 12 '16 at 14:54
  • Those are incorrect anchors for validation. Now, you allow a newline symbol at the end of the string. See http://ideone.com/jsgVlE – Wiktor Stribiżew Aug 12 '16 at 14:55
  • @WiktorStribiżew I tried to overcome the RegEx from accepting a newline symbol at the end but to no avail. Is there a way to possible do that only using RegEx? – ZerosAndOnes Aug 12 '16 at 16:03
  • [Look here](https://msdn.microsoft.com/en-us/library/h5181w5w(v=vs.110).aspx), you will quickly find it. – Wiktor Stribiżew Aug 12 '16 at 16:10
  • @WiktorStribiżew Is it @"\A01[0-9]{9}\z"?Thanks a bunch for increasing my knowledge in any case :D – ZerosAndOnes Aug 12 '16 at 16:17
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if you need regex, try this:

^01[0-9]{9}\z
ROman Ryabko
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    Роман, are you sure? See [this demo](http://regexstorm.net/tester?p=%5e01%5cd%7b9%7d%24&i=01%d9%a1%d9%a2%d9%a3%d9%a4%d9%a5%d9%a6%d9%a7%d9%a8%d9%a9). Also, your regex also allows a newline at the end of the string. – Wiktor Stribiżew Aug 12 '16 at 14:38
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    Nice! ^01[0-9]{9}$ and add singleline flag – ROman Ryabko Aug 12 '16 at 14:50
  • And here is another "nice": http://ideone.com/jsgVlE. As I said, the regex allows a newline at the end of the input. – Wiktor Stribiżew Aug 12 '16 at 14:57
  • Thanks man, it Worked. – Waheed Aug 12 '16 at 15:10
  • There is no need for the `RegexOptions.Singleline` flag, there is no dot anywhere in the pattern. You wanted to say "add `RegexOptions.ECMAScript` flag" - that is a good idea as it will [fix the issue with `\d`](http://regexstorm.net/tester?p=%5e01%5cd%7b9%7d%24&i=01%d9%a1%d9%a2%d9%a3%d9%a4%d9%a5%d9%a6%d9%a7%d9%a8%d9%a9&o=e). Waheed, are you sure you want to allow a string with a newline at the end? – Wiktor Stribiżew Aug 12 '16 at 15:12
  • No definitely not. @Wiktor Stribizew – Waheed Aug 12 '16 at 18:03