Question

i m looking for regex which can extract the date from the following html

<p>British Medical Journal, 29.9.12, pp.37-41.</p>

and convert it in the format 29/09/12

Answer 1

Match this pattern: –

(\d+)[.](\d+)[.](\d+)

and replace with: –

$1/$2/$3

\d is used to match digits. Using it with quantifier (+), you would match one or more digits.
Now, in regex, a dot(.) is a metacharacter, that matches any character. To match a period literally, you would need to either escape it, or use it inside a character class.

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To convert to a specific Date Format, e.g.: – convert 9 -> 09, you can make use of a MatchEvaluator: –

string input = "British Medical Journal, 29.9.12, pp.37-41.";
Regex reg = new Regex(@"(\d+)[.](\d+)[.](\d+)");
string result = reg.Replace(input, delegate(Match m) {
    return m => DateTime.Now.ToString("dd/MM/yy")
});

You can check whether it works or not.