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Get the middle part of a filename using regex

I need a regex that can return up to 10 characters in the middle of a file name.
filename: returns:
msl_0123456789_otherstuff.csv -> 0123456789
msl_test.xml -> test
anythingShort.w1 -> anythingSh
I can capture the beginning and end for removal with the following regex:
Regex.Replace(filename, "(^msl_)|([.][[:alnum:]]{1,3}$)", string.Empty); *
but I also need to have only 10 characters when I am done.
Explanation of the regex above:
(^msl_) - match lines that start with "msl_"
| - or
([.] - match a period
[[:alnum]]{1,3} - followed by 1-3 alphanumeric characters
$) - at the end of the line

Note [[:alnum:]] can't work in a .NET regex, because it does not support POSIX character classes. You may use \w (to match letters, digits, underscores) or [^\W_] (to match letters or digits).
You can use your regex and just keep the first 10 chars in the string:
new string(Regex.Replace(s, #"^msl_|\.\w{1,3}$","").Take(10).ToArray())
See the C# demo online:
var strings = new List<string> { "msl_0123456789_otherstuff.csv", "msl_test.xml", "anythingShort.w1" };
foreach (var s in strings)
{
Console.WriteLine("{0} => {1}", s, new string(Regex.Replace(s, #"^msl_|\.\w{1,3}$","").Take(10).ToArray()));
}
Output:
msl_0123456789_otherstuff.csv => 0123456789
msl_test.xml => test
anythingShort.w1 => anythingSh

Using replace with the alternation, removes either of the alternatives from the start and the end of the string, but it will also work when the extension is not present and does not take the number of chars into account in the middle.
If the file extension should be present you might use a capturing group and make msl_ optional at the beginning.
Then match 1-10 times a word character except the _ followed by matching optional word characters until the .
^(?:msl_)?([^\W_]{1,10})\w*\.[^\W_]{2,}$
.NET regex demo (Click on the table tab)
A bit broader match could be using \S instead of \w and match until the last dot:
^(?:msl_)?(\S{1,10})\S*\.[^\W_]{2,}$
See another regex demo | C# demo
string[] strings = {"msl_0123456789_otherstuff.csv", "msl_test.xml","anythingShort.w1", "123456testxxxxxxxx"};
string pattern = #"^(?:msl_)?(\S{1,10})\S*\.[^\W_]{2,}$";
foreach (String s in strings) {
Match match = Regex.Match(s, pattern);
if (match.Success)
{
Console.WriteLine(match.Groups[1]);
}
}
Output
0123456789
test
anythingSh

Regular expression to find 3 repeated words

I'm trying to create a regular expression which matches the same word 3 times, they are separated by a comma. For example, some inputs would be:
HEY,HEY,HEY - match
NO,NO,NO - match
HEY,HI,HEY - no match
HEY,H,Y - no match
HEY,NO,HEY - no match
How can I go about doing this? I've had a look at some example but they are only good for characters, not words.

This should do the trick:
^(\w+),\1,\1$
Explanation:
^: beginning of the line. Needed to avoid matching "HHEY,HEY,HEY".
(\w+): matches one or more word characters. This is the first catpured group.
,: the character comma.
\1: a backreference to the first captured group. In the other words, matches whatever was matched in (\w+) before.
,: the character comma.
\1: a backreference to the first captured group.
$: end of the line. Needed to avoid matching "HEY,HEY,HEYY".
Source: https://msdn.microsoft.com/en-us/library/az24scfc(v=vs.110).aspx#Anchor_5
Example usage
static void Main()
{
var threeWords = new Regex(#"^(\w+),\1,\1$");
var lines = new[]
{
"HEY,HEY,HEY",
"NO,NO,NO",
"HEY,HI,HEY",
"HEY,H,Y",
"HEY,NO,HEY",
"HHEY,HEY,HEY",
"HEY,HEY,HEYY",
};
foreach (var line in lines)
{
var isMatch = threeWords.IsMatch(line) ? "" : "no ";
Console.WriteLine($"{line} - {isMatch}match");
}
}
Output:
HEY,HEY,HEY - match
NO,NO,NO - match
HEY,HI,HEY - no match
HEY,H,Y - no match
HEY,NO,HEY - no match
HHEY,HEY,HEY - no match
HEY,HEY,HEYY - no match

Regex pattern for splitting a delimited string in curly braces

I have the following string
{token1;token2;token3#somewhere.com;...;tokenn}
I need a Regex pattern, that would give a result in array of strings such as
token1
token2
token3#somewhere.com
...
...
...
tokenn
Would also appreciate a suggestion if can use the same pattern to confirm the format of the string, means string should start and end in curly braces and at least 2 values exist within the anchors.

You may use an anchored regex with named repeated capturing groups:
\A{(?<val>[^;]*)(?:;(?<val>[^;]*))+}\z
See the regex demo
\A - start of string
{ - a {
(?<val>[^;]*) - Group "val" capturing 0+ (due to * quantifier, if the value cannot be empty, use +) chars other than ;
(?:;(?<val>[^;]*))+ - 1 or more occurrences (thus, requiring at least 2 values inside {...}) of the sequence:
; - a semi-colon
(?<val>[^;]*) - Group "val" capturing 0+ chars other than ;
} - a literal }
\z - end of string.
.NET regex keeps each capture in a CaptureCollection stack, that is why all the values captured into "num" group can be accessed after a match is found.
C# demo:
var s = "{token1;token2;token3;...;tokenn}";
var pat = #"\A{(?<val>[^;]*)(?:;(?<val>[^;]*))+}\z";
var caps = new List<string>();
var result = Regex.Match(s, pat);
if (result.Success)
{
caps = result.Groups["val"].Captures.Cast<Capture>().Select(t=>t.Value).ToList();
}

Read it(similar to your problem): How to keep the delimiters of Regex.Split?.
For your RegEx testing use this: http://www.regexlib.com/RETester.aspx?AspxAutoDetectCookieSupport=1.
But RegEx is a very resource-intensive, slow operation.
In your case will be better to use the Split method of string class, for example : "token1;token2;token3;...;tokenn".Split(';');. It will return to you a collection of strings, that you want to obtain.

search string for everything before a set of characters in C#

I'm looking for a way to search a string for everything before a set of characters in C#. For Example, if this is my string value:
This is is a test.... 12345
I want build a new string with all of the characters before "12345".
So my new string would equal "This is is a test.... "
Is there a way to do this?
I've found Regex examples where you can focus on one character but not a sequence of characters.

You don't need to use a Regex:
public string GetBitBefore(string text, string end)
{
var index = text.IndexOf(end);
if (index == -1) return text;
return text.Substring(0, index);
}

You can use a lazy quantifier to match anything, followed by a lookahead:
var match = Regex.Match("This is is a test.... 12345", #".*?(?=\d{5})");
where:
.*? lazily matches everything (up to the lookahead)
(?=…) is a positive lookahead: the pattern must be matched, but is not included in the result
\d{5} matches exactly five digits. I'm assuming this is your lookahead; you can replace it

You can do so with help of regex lookahead.
.*(?=12345)
Example:
var data = "This is is a test.... 12345";
var rxStr = ".*(?=12345)";
var rx = new System.Text.RegularExpressions.Regex (rxStr,
System.Text.RegularExpressions.RegexOptions.IgnoreCase);
var match = rx.Match(data);
if (match.Success) {
Console.WriteLine (match.Value);
}
Above code snippet will print every thing upto 12345:
This is is a test....
For more detail about see regex positive lookahead

This should get you started:
var reg = new Regex("^(.+)12345$");
var match = reg.Match("This is is a test.... 12345");
var group = match.Groups[1]; // This is is a test....
Of course you'd want to do some additional validation, but this is the basic idea.

^ means start of string
$ means end of string
The asterisk tells the engine to attempt to match the preceding token zero or more times. The plus tells the engine to attempt to match the preceding token once or more
{min,max} indicate the minimum/maximum number of matches.
\d matches a single character that is a digit, \w matches a "word character" (alphanumeric characters plus underscore), and \s matches a whitespace character (includes tabs and line breaks).
[^a] means not so exclude a
The dot matches a single character, except line break characters
In your case there many way to accomplish the task.
Eg excluding digit: ^[^\d]*
If you know the set of characters and they are not only digit, don't use regex but IndexOf(). If you know the separator between first and second part as "..." you can use Split()

Take a look at this snippet:
class Program
{
static void Main(string[] args)
{
string input = "This is is a test.... 12345";
// Here we call Regex.Match.
MatchCollection matches = Regex.Matches(input, #"(?<MySentence>(\w+\s*)*)(?<MyNumberPart>\d*)");
foreach (Match item in matches)
{
Console.WriteLine(item.Groups["MySentence"]);
Console.WriteLine("******");
Console.WriteLine(item.Groups["MyNumberPart"]);
}
Console.ReadKey();
}
}

You could just split, not as optimal as the indexOf solution
string value = "oiasjdoiasj12345";
string end = "12345";
string result = value.Split(new string[] { end }, StringSplitOptions.None)[0] //Take first part of the result, not the quickest but fairly simple

Regex to match and return group names

I need to match the following strings and returns the values as groups:
abctic
abctac
xyztic
xyztac
ghhtic
ghhtac
Pattern is wrote with grouping is as follows:
(?<arch>[abc,xyz,ghh])(?<flavor>[tic,tac]$)
The above returns only parts of group names. (meaning match is not correct).
If I use * in each sub pattern instead of $ at the end, groups are correct, but that would mean that abcticff will also match.
Please let me know what my correct regex should be.

Your pattern is incorrect because a pipe symbol | is used to specify alternate matches, not a comma in brackets as you were using, i.e., [x,y].
Your pattern should be: ^(?<arch>abc|xyz|ghh)(?<flavor>tic|tac)$
The ^ and $ metacharacters ensures the string matches from start to end. If you need to match text in a larger string you could replace them with \b to match on a word boundary.
Try this approach:
string[] inputs = { "abctic", "abctac", "xyztic", "xyztac", "ghhtic", "ghhtac" };
string pattern = #"^(?<arch>abc|xyz|ghh)(?<flavor>tic|tac)$";
foreach (var input in inputs)
{
var match = Regex.Match(input, pattern);
if (match.Success)
{
Console.WriteLine("Arch: {0} - Flavor: {1}",
match.Groups["arch"].Value,
match.Groups["flavor"].Value);
}
else
Console.WriteLine("No match for: " + input);
}