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How to remove multiple first characters using regex?

I have string string A = "... :-ggw..-:p";
using regex: string B = Regex.Replace(A, #"^\.+|:|-|", "").Trim();
My Output isggw..p.
What I want is ggw..-:p.
Thanks

You may use a character class with your symbols and whitespace shorthand character class:
string B = Regex.Replace(A, #"^[.:\s-]+", "");
See the regex demo
Details
^ - start of string
[.:\s-]+ - one or more characters defined in the character class.
Note that there is no need escaping . inside [...]. The - does not have to be escaped since it is at the end of the character class.

A regex isn't necessary if you only want to trim specific characters from the start of a string. System.String.TrimStart() will do the job:
var source = "... :-ggw..-:p";
var charsToTrim = " .:-".ToCharArray();
var result = source.TrimStart(charsToTrim);
Console.WriteLine(result);
// Result is 'ggw..-:p'

c# How do trim all non numeric character in a string

what is the faster way to trim all alphabet in a string that have alphabet prefix.
For example, input sting "ABC12345" , and i wish to havee 12345 as output only.
Thanks.

Please use "char.IsDigit", try this:
static void Main(string[] args)
{
var input = "ABC12345";
var numeric = new String(input.Where(char.IsDigit).ToArray());
Console.Read();
}

You can use Regular Expressions to trim an alphabetic prefix
var input = "ABC123";
var trimmed = Regex.Replace(input, #"^[A-Za-z]+", "");
// trimmed = "123"
The regular expression (second parameter) ^[A-Za-z]+ of the replace method does most of the work, it defines what you want to be replaced using the following rules:
The ^ character ensures a match only exists at the start of a string
The [A-Za-z] will match any uppercase or lowercase letters
The + means the upper or lowercase letters will be matched as many times in a row as possible
As this is the Replace method, the third parameter then replaces any matches with an empty string.

The other answers seem to answer what is the slowest way .. so if you really need the fastest way, then you can find the index of the first digit and get the substring:
string input = "ABC12345";
int i = 0;
while ( input[i] < '0' || input[i] > '9' ) i++;
string output = input.Substring(i);
The shortest way to get the value would probably be the VB Val method:
double value = Microsoft.VisualBasic.Conversion.Val("ABC12345"); // 12345.0

You would have to regular expression. It seems you are looking for only digits and not letters.
Sample:
string result =
System.Text.RegularExpressions.Regex.Replace("Your input string", #"\D+", string.Empty);

REGEX Adding a string before comma c#

How can I append a known string before each coma on a comma separated string.
Is there a regex for that or something that doesn't use a loop
EX
given string :
email, email2, email3 (etc...)
to
string suffix = "#iou.com"
string desiredResult = "email#iou.com, email2#iou.com, email3#iou.com
Thank you!!

You can use [^,\s]+ regexp, and replace with "$0"+suffix:
var res = Regex.Replace(original, #"[^,\s]+", "$0"+suffix);
"$0" refers to the content captured by the regular expression.
Demo.

Or using LINQ:
Console.WriteLine(string.Join(",",input.Split(',').Select(s => string.Concat(s, suffix))));

You could use a zero-length capture group. Here's how that might look:
\w+(?<ReplaceMe>),?
The \w matches alphanumeric characters, and the named capture group called "ReplaceMe" matches the zero-length space between the end of the word and the beginning of the comma (or any other non-alphanumeric item, including the end of the string).
Then you'd just replace ReplaceMe with the appended value, like this:
Regex.Replace(original, #"\w+(?<ReplaceMe>),?", "#email.com");
Here's an example ofthat regex in action.

Here you are:
string input = "email, email2, email3";
string suffix = "#iou.com";
//string desiredResult = "email#iou.com, email2#iou.com, email3#iou.com";
Console.WriteLine(Regex.Replace((input + ",")
.Replace(",", suffix + ","), #",$", ""));
Hope this helps.

Remove dot character from a String C#

Assume I have a string "2.36" and I want it trimmed to "236"
I used Trim function in example
String amount = "2.36";
String trimmedAmount = amount.Trim('.');
The value of trimmedAmount is still 2.36
When amount.Trim('6'); it works perfectly but with '.'
What I am doing wrong?
Thanks a lot
Cheers

Trimming is removing characters from the start or end of a string.
You are simply trying to remove the ., which can be done by replacing that character with nothing:
string cleanAmount = amount.Replace(".", string.Empty);

If you want to remove everything but the digits:
String trimmedAmount = new String(amount.Where(Char.IsDigit).ToArray());
or:
String trimmedAmount = Regex.Replace(amount, #"\D+", String.Empty);

String.Trim removes leading and trailing whitespace. You need to use String.Replace()
Like:
string amount = "2.36";
string newAmount = amount.Replace(".", "");

Two ways :
string sRaw = "5.32";
string sClean = sRaw.Replace(".", "");
Trim is make for removing leading and trailings characters (such as space by default).

Regex to match alphanumeric and spaces

What am I doing wrong here?
string q = "john s!";
string clean = Regex.Replace(q, #"([^a-zA-Z0-9]|^\s)", string.Empty);
// clean == "johns". I want "john s";

just a FYI
string clean = Regex.Replace(q, #"[^a-zA-Z0-9\s]", string.Empty);
would actually be better like
string clean = Regex.Replace(q, #"[^\w\s]", string.Empty);

This:
string clean = Regex.Replace(dirty, "[^a-zA-Z0-9\x20]", String.Empty);
\x20 is ascii hex for 'space' character
you can add more individual characters that you want to be allowed.
If you want for example "?" to be ok in the return string add \x3f.

I got it:
string clean = Regex.Replace(q, #"[^a-zA-Z0-9\s]", string.Empty);
Didn't know you could put \s in the brackets

The following regex is for space inclusion in textbox.
Regex r = new Regex("^[a-zA-Z\\s]+");
r.IsMatch(textbox1.text);
This works fine for me.

I suspect ^ doesn't work the way you think it does outside of a character class.
What you're telling it to do is replace everything that isn't an alphanumeric with an empty string, OR any leading space. I think what you mean to say is that spaces are ok to not replace - try moving the \s into the [] class.

There appear to be two problems.
You're using the ^ outside a [] which matches the start of the line
You're not using a * or + which means you will only match a single character.
I think you want the following regex #"([^a-zA-Z0-9\s])+"

bottom regex with space, supports all keyboard letters from different culture
string input = "78-selim güzel667.,?";
Regex regex = new Regex(#"[^\w\x20]|[\d]");
var result= regex.Replace(input,"");
//selim güzel

The circumflex inside the square brackets means all characters except the subsequent range. You want a circumflex outside of square brackets.

This regex will help you to filter if there is at least one alphanumeric character and zero or more special characters i.e. _ (underscore), \s whitespace, -(hyphen)
string comparer = "string you want to compare";
Regex r = new Regex(#"^([a-zA-Z0-9]+[_\s-]*)+$");
if (!r.IsMatch(comparer))
{
return false;
}
return true;
Create a set using [a-zA-Z0-9]+ for alphanumeric characters, "+" sign (a quantifier) at the end of the set will make sure that there will be at least one alphanumeric character within the comparer.
Create another set [_\s-]* for special characters, "*" quantifier is to validate that there can be special characters within comparer string.
Pack these sets into a capture group ([a-zA-Z0-9]+[_\s-]*)+ to say that the comparer string should occupy these features.

[RegularExpression(#"^[A-Z]+[a-zA-Z""'\s-]*$")]
Above syntax also accepts space