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Regex pattern not working on my C# code however it works on an online tester

I want to extract the double value from the string that contains a specific keyword. For example:
Amount : USD 3,747,190.67
I need to extract the value "3,747,190.67" from the string above using the keyword Amount, for that I tested this pattern in different online Regex testers and it works:
(?<=\bAmount.*)(\d+\,*\.*)*
However it doesn't work on my C# code:
if (type == typeof(double))
{
double doubleVal = 0;
pattern = #"(?<=\bAmount.*)(\d+\,*\.*)*";
matchPattern = Regex.Match(textToParse, pattern);
if (matchPattern.Success)
{
double.TryParse(matchPattern.Value.ToString(), out doubleVal);
}
return doubleVal;
}

This one works:
(?<=\bAmount.*)\d+(,\d+)*(\.\d+)?
(?<=\bAmount.*) the look behind
\d+                      leading digits (at least one digit)
(,\d+)*               thousands groups (zero or more times)
(\.\d+)?             decimals (? = optional)
Note that the regex tester says "9 matches found" for your pattern. For my pattern it says "1 match found".
The problem with your pattern is that its second part (\d+\,*\.*)* can be empty because of the * at the end. The * quantifier means zero, one or more repetitions. Therefore, the look-behind finds 8 empty entries between Amount and the number. The last of the 9 matches is the number. You can correct it by replacing the * with a +. See: regextester with *, regextester with +. You can also test it with "your" tester and switch to the table to see the detailed results.
My solution does not allow consecutive commas or points but allows numbers without thousands groups or a decimal part.

The lookbehind (?<=\bAmount.*) is always true in the example data after Amount.
The first 7 matches are empty, as (\d+\,*\.*)* can not consume a character where there is no digit, but it matches at the position as the quantifier * matches 0 or more times.
See this screenshot of the matches:
You might use
(?<=\bAmount\D*)\d{1,3}(?:,\d{3})*(?:\.\d{1,2})?\b
(?<=\bAmount\D*) Positive lookbehind, assert Amount to the left followed by optional non digits
\d{1,3} Match 1-3 digits
(?:,\d{3})* Optionally repeat , and 3 digits
(?:\.\d{1,2})? Optionally match . and 1 or 2 digits
\b A word boundary
See a .NET regex demo
For example
double doubleVal = 0;
var pattern = #"(?<=\bAmount\D*)\d{1,3}(?:,\d{3})*(?:\.\d{1,2})?\b";
var textToParse = "Amount : USD 3,747,190.67";
var matchPattern = Regex.Match(textToParse, pattern);
if (matchPattern.Success)
{
double.TryParse(matchPattern.Value.ToString(), out doubleVal);
}
Console.WriteLine(doubleVal);
Output
3747190.67
You can omit the word boundaries if needed if a partial match is also valid
(?<=Amount\D*)\d{1,3}(?:,\d{3})*(?:\.\d{1,2})?

Retrieving digits from a string with a certain pattern

I have a string value of:
"Drop 1.0.2.34 - Compatible with core revision 123456"
And I am trying to get the value 1.0.2.34 with the full stops from the string.
I am using Regex to try and get it, but it returns with a "" value.
Ex.
Match match = Regex.Match(string, "([0-9]*[.][0-9]*)*");
if (match.Success)
{
string version = match.Captures[0].Value;
}
I think there is something small that I am missing because it does find a match in the string, but it doesn't have a value. Can someone please help?

Your regex matches an empty string, and since you are only looking for 1 match, it returns the empty string beofre the first char.
Use
[0-9]+(?:\.[0-9]+)+
See the regex demo
Details:
[0-9]+ - 1+ digits
(?:\.[0-9]+)+ - 1+ sequences of:
\. - a dot
[0-9]+ - 1+ digits.
C#:
string version = string.Empty;
Match match = Regex.Match(string, #"[0-9]+(?:\.[0-9]+)+");
if (match.Success)
{
version = match.Value;
}

Replace special characters or special characters followed by space

I have this particular string:
Administrationsomkostninger I -2.889 - r0.l l0
I would like to replace these characters:r,l and i with 1.
I use this expression:
([(t|r|l|i|)])
That gives me this string:
Adm1n1s11a11onsomkos1n1nge1 1 -2.889 - 10.1 10
Now i want to replace the all digits that contains a digit followed + a whitespace
so in this case only - 10.1 10 gets converted to -10.110

Try this
string input = "Administrationsomkostninger I -2.889 - r0.l l0";
string pattern = #"(?'spaces'\s){2,}";
string output = Regex.Replace(input, pattern, " ");
​

How do I write regex to validate EIN numbers?

I want to validate that a string follows this format (using regex):
valid: 123456789 //9 digits
valid: 12-1234567 // 2 digits + dash + 7 digits
Here's an example, how I would use it:
var r = new Regex("^[1-9]\d?-\d{7}$");
Console.WriteLine(r.IsMatch("1-2-3"));
I have the regex for the format with dash, but can't figure how to include the non-dash format???

Regex regex = new Regex("^\\d{2}-?\\d{7}$");
This will accept the two formats you want: 2 digits then an optional dash and 7 numbers.

^ \d{9} | \d{2} - \d{7} $
Remove the spaces, they are there for readability.

Removing sequence of numbers from Readline with Regex

I have the following sample string:
string s = Console.ReadLine();
s= {6} {7613023456148 } {7.040 } {56780} {Sample String}
How do I achieve the following with regex or something similar:
Remove all numbers in a line that start with 7 and are 13 digits long.
Remove all decimal numbers.
Output
s = {6} {56780} {Sample String}

You can replace the captured string use following regex with an empty string :
7\d{12}|\d\.\d+
But Note that if your numbers are within {} you need :
\b{\s*7\d{12}\s*}\b|\b{\s*\d+\.\d+\s*}\b
See demo https://regex101.com/r/dL1vF4/1

You are looking for this regex:
var s = "{6} {7613023456148 } {7.040 } {56780} {Sample String}";
s = Regex.Replace(s, #"\s*{(?:\s*7[0-9]{12}\s*|\d+\.\d+\s*)}", string.Empty);
Console.WriteLine(s); // ==> "{6} {56780} {Sample String}"
See IDEONE demo
REGEX matches 2 alternatives inside {...} that is preceded with optional whitespace (\s*):
\s*7[0-9]{12}\s* - optional whitespace followed with7`, then 12 digits and optional whitespace
\d+\.\d+\s* - 1 or more digits, a . decimal separator, again 1 or more digits, and optional whitespace.
Since all your values are inside {...}, you need no word boundaries.