Issue with string matching the Regex pattern and replacing with matched

Question

Requirement is that the string variable text2 containing table data having dd/mm/yyyy hh:mm format need's to replace the date and time enclosed with double quotes with ="dd-MMM-yyyy HH:mm:ss"

Eg: 25-Feb-2020 15:27:58 need to be replaced with ="25-Feb-2020 15:27:58"

DotNetFiddler

Here is the complete snippet of code shown below

using System;
using System.Text.RegularExpressions;


public class Program
{
    public static void Main()
    {
        string text = "<table>\n  <thead><tr><th style=\"\"><div class=\"th-inner \">Login Name</div><div class=\"fht-cell\"></div></th><th style=\"\"><div class=\"th-inner sortable\">Registered</div><div class=\"fht-cell\"></div></th><th style=\"\"><div class=\"th-inner \">Registered Date <br>Time</div><div class=\"fht-cell\"></div></th><th style=\"\"><div class=\"th-inner sortable\">User Response Count</div><div class=\"fht-cell\"></div></th><th style=\"\"><div class=\"th-inner \">Test Start Date Time</div><div class=\"fht-cell\"></div></th><th style=\"\"><div class=\"th-inner \">Test End Date Time</div><div class=\"fht-cell\"></div></th><th style=\"\"><div class=\"th-inner \">Time Remaining</div><div class=\"fht-cell\"></div></th><th style=\"\"><div class=\"th-inner \">User Status</div><div class=\"fht-cell\"></div></th></tr></thead><tbody><tr data-index=\"9\"><td style=\"\">njuser14</td><td style=\"\">Yes</td><td style=\"\">-</td><td style=\"\">0</td><td style=\"\">29-Feb-2020 15:27:58</td><td style=\"\">29-Feb-2020 15:28:03</td><td style=\"\">179</td><td style=\"\">Paused</td></tr><tr data-index=\"10\"><td style=\"\">njuser15</td><td style=\"\">Yes</td><td style=\"\">-</td><td style=\"\">0</td><td style=\"\">29-Feb-2020 15:27:32</td><td style=\"\">29-Feb-2020 15:27:42</td><td style=\"\">179</td><td style=\"\">Paused</td></tr></tbody></table>";
        string text2 = " dasd arew 2017-03-11 12:25:56 2017-03-11 12:25:56 das tfgwe 2017-03-11 12:25:56 ";
        string pattern = @"\d{4}\-\d{2}\-\d{2}\s\d{2}\:\d{2}\:\d{2}";
        Regex r = new Regex(pattern);
        var res = r.Replace(text, new MatchEvaluator(ConvertDateFormat));
        var res2 = r.Replace(text2, new MatchEvaluator(ConvertDateFormat));
        Console.WriteLine(res);
        Console.WriteLine("-------------------------------------------------------");
        Console.WriteLine(res2);
    }

    static string ConvertDateFormat(Match m)
    {
        var mydate = DateTime.Parse(m.Value);
        return mydate.ToString("=yyyy-MM-dd hh:mm:ss");
    }
}

// 29-Feb-2020 15:27:58 need to be replaced with ="29-Feb-2020 15:27:58"

Results:

<table>
  <thead><tr><th style=""><div class="th-inner ">Login Name</div><div class="fht-cell"></div></th><th style=""><div class="th-inner sortable">Registered</div><div class="fht-cell"></div></th><th style=""><div class="th-inner ">Registered Date <br>Time</div><div class="fht-cell"></div></th><th style=""><div class="th-inner sortable">User Response Count</div><div class="fht-cell"></div></th><th style=""><div class="th-inner ">Test Start Date Time</div><div class="fht-cell"></div></th><th style=""><div class="th-inner ">Test End Date Time</div><div class="fht-cell"></div></th><th style=""><div class="th-inner ">Time Remaining</div><div class="fht-cell"></div></th><th style=""><div class="th-inner ">User Status</div><div class="fht-cell"></div></th></tr></thead><tbody><tr data-index="9"><td style="">njuser14</td><td style="">Yes</td><td style="">-</td><td style="">0</td><td style="">29-Feb-2020 15:27:58</td><td style="">29-Feb-2020 15:28:03</td><td style="">179</td><td style="">Paused</td></tr><tr data-index="10"><td style="">njuser15</td><td style="">Yes</td><td style="">-</td><td style="">0</td><td style="">29-Feb-2020 15:27:32</td><td style="">29-Feb-2020 15:27:42</td><td style="">179</td><td style="">Paused</td></tr></tbody></table>
-------------------------------------------------------
 dasd arew =2017-03-11 12:25:56 =2017-03-11 12:25:56 das tfgwe =2017-03-11 12:25:56

But here the string variable

text2 value is being replaced to =dd-MMM-yyyy HH:mm:ss. But not to "=dd-MMM-yyyy HH:mm:ss"
text value remains same. But not to "=dd-MMM-yyyy HH:mm:ss"

Are you expecting the double quotes in ToString("=yyyy-MM-dd hh:mm:ss") to be included in your replaced text? — Peter M
– Peter M, Commented Mar 31, 2020 at 13:27
@PeterM Yes. But how would you make to put ToString("="yyyy-MM-dd hh:mm:ss""); — Nɪsʜᴀɴᴛʜ ॐ
– Nɪsʜᴀɴᴛʜ ॐ, Commented Mar 31, 2020 at 13:31
string.Format("=\"{0}\"", mydate.ToString("yyyy-MM-dd hh:mm:ss")) — user5386938
– user5386938, Commented Mar 31, 2020 at 13:32
Tried. But that wouldn't accomplish for text Click here @JustinEzequiel — Nɪsʜᴀɴᴛʜ ॐ
– Nɪsʜᴀɴᴛʜ ॐ, Commented Mar 31, 2020 at 13:41
If you had not hidden the other datetime string format in the too long text variable, then I'd have seen that you had two different formats that you were trying to match with one regular expression. Try string pattern = @"(?:\d{4}\-\d{2}\-\d{2}\s\d{2}\:\d{2}\:\d{2})|(?:\d{2}-[A-Z][a-z]{2}-\d{4} \d{2}\:\d{2}\:\d{2})"; — user5386938
– user5386938, Commented Mar 31, 2020 at 18:08

Peter M · Accepted Answer · 2020-03-31 14:16:56Z

As per the comments, the first issue seems to be the expectation that

return mydate.ToString("=yyyy-MM-dd hh:mm:ss");

Will include the quotes when it converts the DataTime format to a string. But these quotes are actually the terminators of th format string itself, and are not a part of the format string.

The solution to that is as suggested by Justin

string.Format("=\"{0}\"", mydate.ToString("yyyy-MM-dd hh:mm:ss"))

Although my preferred format would use string interpolation

$"\"{mydate.ToString("yyyy-MM-dd hh:mm:ss")}\""

The second issue is that text and text2 have differing date time formats, and the supplied regex only matches the formats in text2

text:  29-Feb-2020 15:27:58 
text2: 2017-03-11 12:25:56 
regex: @"\d{4}\-\d{2}\-\d{2}\s\d{2}\:\d{2}\:\d{2}"

Regexes match strings and are not aware of the data that they are matching. So a naive regex for text would be something like (untested)

@"\d{2}\-[a-zA-Z]{3}\-\d{4}\s\d{2}\:\d{2}\:\d{2}"

This assumes that the months are always 3 chars long, and that there is nothing that looks like a date that is not a date.

Your example explicitly does 2 different matches, so if that is how you do things then you could create a new regex for each of text and text2 and do multiple replacements. Or you could try combining the regexes like (untested):

@"\d{4}\-\d{2}\-\d{2}\s\d{2}\:\d{2}\:\d{2}|\d{2}\-[a-zA-Z]{3}\-\d{4}\s\d{2}\:\d{2}\:\d{2}"

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