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trim string before character but still keep the remain part after it

So I have this string which I have to trim and manipulate a little with it.
My string example:
string test = "studentName_123.pdf";
Now, what I want to do is somehow extract only the _123 part and at the end I need to have studentName.pdf
What I have tried:
string test_extracted = test.Substring(0, test.LastIndexOf("_") )+".pdf";
This also works but the thing is that I don't want to add the ".pdf" suffix at the end of the string manually because I can have strings that are not pdf, for ex. studentName.docx , studentName.png.
So basically I just want the "_123" part removed but still keep the remain part after that.

I think this might help you:
string test = "studentName_123.pdf";
string test_extracted = test.Substring(0, test.LastIndexOf("_") )+ test.Substring(test.LastIndexOf("."),test.Length - test.LastIndexOf(".") );
Using Remove(int startIndex, int count):
string test = "studentName_123.pdf";
string test_extracted = test.Remove(test.LastIndexOf("_"), test.LastIndexOf(".") - test.LastIndexOf("_"));

Sounds like you mean something like this?
string extension = Path.GetExtension(test);
string pdfName = Path.GetFileNameWithoutExtension(test).Split('_')[0];
string fullName = pdfName + extension;

Since you know what value you will always be replacing in your strings, "_123", to base on your example, just utilize the replace method and replace it with nothing since the method expects two arguments;
string test_extracted = test.replace('_123', '');

This could be solved with a regular expression like this
(\w*)_.*(\.\w*) where the first capture group (\w*) matches everything before the underscore and the second group (\.\w*) matches the file extensions.
Lastly we just have to concat the groups without the stuff inbetween like so:
string test = "studentName_123.pdf";
var regex = Regex.Match(test, #"(\w*)_.*(\.\w*)");
string newString = regex.Groups[1].Value + regex.Groups[2].Value;

Shorthand way to remove last forward slash and trailing characters from string

If I have the following string:
/lorem/ipsum/dolor
and I want this to become:
/lorem/ipsum
What is the short-hand way of removing the last forward slash, and all characters following it?
I know how I can do this by spliting the string into a List<> and removing the last item, and then joining, but is there a shorter way of writing this?
My question is not URL specific.

You can use Substring() and LastIndexOf():
str = str.Substring(0, str.LastIndexOf('/'));
EDIT (suggested comment)
To prevent any issues when the string may not contain a /, you could use something like:
int lastSlash = str.LastIndexOf('/');
str = (lastSlash > -1) ? str.Substring(0, lastSlash) : str;
Storing the position in a temp-variable would prevent the need to call .LastIndexOf('/') twice, but it could be dropped in favor of a one-line solution instead.

If there is '/' at the end of the url, remove it.
If not; just return the original one.
var url = this.Request.RequestUri.ToString();
url = url.EndsWith("/") ? url.Substring(0, url.Length - 1) : url;
url += #"/mycontroller";

You can do something like str.Remove(str.LastIndexOf("/")), but there is no built-in method to do what you want.
Edit: you could also use the Uri object to traverse directories, although it does not give exactly what you want:
Uri baseUri = new Uri("http://domain.com/lorem/ipsum/dolor");
Uri myUri = new Uri(baseUri, ".");
// myUri now contains http://domain.com/lorem/ipsum/

One simple way would be
String s = "domain.com/lorem/ipsum/dolor";
s = s.Substring(0, s.LastIndexOf('/'));
Console.WriteLine(s);
Another maybe
String s = "domain.com/lorem/ipsum/dolor";
s = s.TrimEnd('/');
Console.WriteLine(s);

You can use the regex /[^/]*$ and replace with the empty string:
var fixed = new Regex("/[^/]*$").Replace("domain.com/lorem/ipsum/dolor", "")
But it's probably overkill here. #newfurniturey's answer of Substring with LastIndexOf is probably best.

I like to create a String Extension for stuff like this:
/// <summary>
/// Returns with suffix removed, if present
/// </summary>
public static string TrimIfEndsWith(
this string value,
string suffix)
{
return
value.EndsWith(suffix) ?
value.Substring(0, value.Length - suffix.Length) :
value;
}
You can then use like this:
var myString = "/lorem/ipsum/dolor";
myStringClean = myString.TrimIfEndsWith("/dolor");
You now have a re-usable extension across all of your projects that can be used to remove one trailing character or multiple.

using System.IO;
mystring.TrimEnd(Path.AltDirectorySeparatorChar); // To remove "/"
mystring.TrimEnd(Path.DirectorySeparatorChar); // To remove "\"

while (input.Last() == '/' || input.Last() == '\\')
{
input = input.Substring(0, input.Length - 1);
}

Thank you #Curt for your question.
I slightly improved #newfurniturey's code, and here is my version.
if(str.Contains('/')){
str = str.Substring(0, str.LastIndexOf('/'));
}

I'm way late to the party, but if you're using C# 8.0+, another clean approach would be to use the range operator:
if (urlStr.EndsWith("/")) urlStr = urlStr[..^1];
If you're curious as to how this works, take a look at the spec for ranges in C#:
https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-8.0/ranges
tldr; urlStr[..^1] roughly translates to something along the lines of "Give me a substring comprised of the characters contained within the range of index 0 to whatever index is 1 away from the last index.".
In other words, it's similar to...
urlStr.Substring(0, urlStr.Length-1)

replace a character in a string in c# based on position with a string

I want to replace a charecter in a string with a string in c#.
I have tried the following,
Here in the following program, i want replace set of charecters between charecters ':' and first occurance of '-' with some others charecters.
I could able to extract the set of charecters between ':' and first occurance of '-'.
Can any one say how to insert these back in the source string.
string source= "tcm:7-426-8";
string target= "tcm:10-15-2";
int fistunderscore = target.IndexOf("-");
string temp = target.Substring(4, fistunderscore-4);
Response.Write("<BR>"+"temp1:" + temp + "<BR>");
Examples:
source: "tcm:7-426-8" or "tcm:100-426-8" or "tcm:10-426-8"
Target: "tcm:10-15-2" or "tcm:5-15-2" or "tcm:100-15-2"
output: "tcm:10-426-8" or "tcm:5-426-8" or "tcm:100-426-8"
In a nutshell, I want to replace the set of charectes between ':' and '-'(firstoccurance) and the charecters extracetd from the same sort of string.
Can any help how it can be done.
Thank you.

If you want to replace the first ":Number-" from the source with the content from target, you can use the following regex.
var pattern1 = New Regex(":\d{1,3}-{1}");
if(pattern1.IsMatch(source) && pattern1.IsMatch(target))
{
var source = "tcm:7-426-8";
var target = "tcm:10-15-2";
var res = pattern1.Replace(source, pattern1.Match(target).Value);
// "tcm:10-426-8"
}
Edit: To not have your string replaced with something empty, add an if-clause before the actualy replacing.

Try a regex solution - first this method, takes the source and target strings, and performs a regex replace on the first, targetting the first numbers after the 'tcm', which must be anchored to the start of the string. In the MatchEvaluator it executes the same regex again, but on the target string.
static Regex rx = new Regex("(?<=^tcm:)[0-9]+", RegexOptions.Compiled);
public string ReplaceOneWith(string source, string target)
{
return rx.Replace(source, new MatchEvaluator((Match m) =>
{
var targetMatch = rx.Match(target);
if (targetMatch.Success)
return targetMatch.Value;
return m.Value; //don't replace if no match
}));
}
Note that no replacement is performed if the regex doesn't return a match on the target string.
Now run this test (probably need to copy the above into the test class):
[TestMethod]
public void SO9973554()
{
Assert.AreEqual("tcm:10-426-8", ReplaceOneWith("tcm:7-426-8", "tcm:10-15-2"));
Assert.AreEqual("tcm:5-426-8", ReplaceOneWith("tcm:100-426-8", "tcm:5-15-2"));
Assert.AreEqual("tcm:100-426-8", ReplaceOneWith("tcm:10-426-8", "tcm:100-15-2"));
}

I'm not clear on the logic used to decide which bit from which string is used, but still, you should use Split(), rather than mucking about with string offsets:
(note that the Remove(0,4) is there to remove the tcm: prefix)
string[] source = "tcm:90-2-10".Remove(0,4).Split('-');
string[] target = "tcm:42-23-17".Remove(0,4).Split('-');
Now you have the numbers from both source and target in easy-to-access arrays, so you can build the new string any way you want:
string output = string.Format("tcm:{0}-{1}-{2}", source[0], target[1], source[2]);

Heres without regex
string source = "tcm:7-426-8";
string target = "tcm:10-15-2";
int targetBeginning = target.IndexOf("-");
int sourceBeginning = source.IndexOf("-");
string temp = target.Substring(0, targetBeginning);//tcm:10
string result = temp + source.Substring(sourceBeginning, source.Length-sourceBeginning); //tcm:10 + -426-8

How to remove all instances of a specific character from a string?

I am trying to remove all of a specific character from a string. I have been using String.Replace, but it does nothing, and I don't know why. This is my current code:
if (Gamertag2.Contains("^"))
{
Gamertag2.Replace("^" + 1, "");
}
This just leaves the string as it was before. Can anyone please explain to me as to why?

You must assign the return value of String.Replace to your original string instance:
hence instead of(no need for the Contains check)
if (Gamertag2.Contains("^"))
{
Gamertag2.Replace("^" + 1, "");
}
just this(what's that mystic +1?):
Gamertag2 = Gamertag2.Replace("^", "");

Two things:
1) C# Strings are immutable. You'll need to do this :
Gamertag2 = Gamertag2.Replace("^" + 1, "");
2) "^" + 1? Why are you doing this? You are basically saying Gamertag2.Replace("^1", ""); which I'm sure is not what you want.

Like climbage said, your problem is definitely
Gamertag2.Replace("^"+1,"");
That line will only remove instances of "^1" from your string. If you want to remove all instances of "^", what you want is:
Gamertag2.Replace("^","");

I know this thread is old and also that my solution may be inefficient to the extreme, but it replaces all occurrences of a string. Found that if I was looking for "\r\n\r\n\r\n" to replace with "\r\n\r\n" a single Replace() didn't catch all.
Therefor this:
do // First get rid of spaces like " \r"
{
str = str.Replace(" \r","\r")
} while (str.Cointains(" \r"));
do // Then remove the CrLf's in surplus.
{
str = str.Replace("\r\n\r\n\r\n","\r\n\r\n")
} while (str.Cointains("\r\n\r\n\r\n"));

get all characters to right of last dash

I have the following:
string test = "9586-202-10072"
How would I get all characters to the right of the final - so 10072. The number of characters is always different to the right of the last dash.
How can this be done?

You can get the position of the last - with str.LastIndexOf('-'). So the next step is obvious:
var result = str.Substring(str.LastIndexOf('-') + 1);
Correction:
As Brian states below, using this on a string with no dashes will result in the original string being returned.

You could use LINQ, and save yourself the explicit parsing:
string test = "9586-202-10072";
string lastFragment = test.Split('-').Last();
Console.WriteLine(lastFragment);

I can see this post was viewed over 46,000 times. I would bet many of the 46,000 viewers are asking this question simply because they just want the file name... and these answers can be a rabbit hole if you cannot make your substring verbatim using the at sign.
If you simply want to get the file name, then there is a simple answer which should be mentioned here. Even if it's not the precise answer to the question.
result = Path.GetFileName(fileName);
see https://msdn.microsoft.com/en-us/library/system.io.path.getfilename(v=vs.110).aspx

string tail = test.Substring(test.LastIndexOf('-') + 1);

YourString.Substring(YourString.LastIndexOf("-"));

With the latest C# 8 and later you can use Range Indexer as follows:-
string test = "9586-202-10072"
var foo = test?[(test.LastIndexOf('-') + 1)..];
// foo is => 10072

string atest = "9586-202-10072";
int indexOfHyphen = atest.LastIndexOf("-");
if (indexOfHyphen >= 0)
{
string contentAfterLastHyphen = atest.Substring(indexOfHyphen + 1);
Console.WriteLine(contentAfterLastHyphen );
}

See String.lastIndexOf method

I created a string extension for this, hope it helps.
public static string GetStringAfterChar(this string value, char substring)
{
if (!string.IsNullOrWhiteSpace(value))
{
var index = value.LastIndexOf(substring);
return index > 0 ? value.Substring(index + 1) : value;
}
return string.Empty;
}

test.Substring[(test.LastIndexOf('-') + 1)..]
C# 8 (late 2019) introduces range operator and simplifies it a bit further. The two dots here means from the index (inclusive) till the end of string.

test.Substring(test.LastIndexOf("-"))

and... in case you need the left part of a string:
private string AllTheLeftPart(string theString)
{
string rightPart = theString.Substring(theString.LastIndexOf('-') + 1);
string leftPart theString.Replace("-" + rightPart, String.Empty);
return leftPart ;
}