c# Regex to match all Sri Lankan phone numbers

Question

I didn't find any on google on the regex expression for Sri Lankan phone numbers; The formats are:

1. 775645645 (9 digits)
2. 0775645645 (10 digits)
3. +94775645645

It should start with 7 or 0 or +94. Can anyone help me with this. Appreciate your solutions.

Answer 1

Let's build the pattern:

 ^            - anchor (string start)
 7|0|(?:\+94) - either 7 or 0 or +94
[0-9]{9,10}   - from 9 up and including to 10 digits (chars on [0-9] range)
 $            - anchor (string end)

So we have

  string pattern = @"^(?:7|0|(?:\+94))[0-9]{9,10}$";

Tests:

string[] tests = new string[] {
  "775645645",
  "0775645645",
  "+94775645645",
  "123456669",
  "1234566698888",
  "+941234566698888",
  "+94123456"
};

string pattern = @"^(?:7|0|(?:\+94))[0-9]{9,10}$";

string report = string.Join(Environment.NewLine, tests
  .Select(item => $"{item,-20} : {(Regex.IsMatch(item, pattern) ? "Matched" : "Not")}"));

Console.Write(report);

Outcome:

775645645            : Matched
0775645645           : Matched
+94775645645         : Matched
123456669            : Not
1234566698888        : Not
+941234566698888     : Not
+94123456            : Not