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Building a regular expression in C#

How to check the following text in C# with Regex:
key_in-get { 43243225543543543 };
or
key_in_set { password123 : 34980430943834 };
I tried to build a regular expression, but I failed after few hours.
Here is my code:
string text1 = "key_in-get { 322389238237 };";
string text2 = "key_in-set { password123 : 322389238237 };";
string pattern = "key_in-(get|set) { .* };";
var result1 = Regex.IsMatch(text, pattern);
Console.Write("Is valid: {0} ", result1);
var result2 = Regex.IsMatch(text, pattern);
Console.Write("Is valid: {0} ", result2);
I have to check if there is "set" or "get".
If the pattern finds "set" then it can only accept following pattern "text123 : 123456789", and if it finds "get" then should accept only "123456789".

You can use
key_in-(?:get|(set)) {(?(1) \w+ :) \w+ };
key_in-(?:get|(set))\s*{(?(1)\s*\w+\s*:)\s*\w+\s*};
key_in-(?:get|(set))\s*{(?(1)\s*\w+\s*:)\s*\d+\s*};
See the regex demo. The second one allows any amount of any whitespace between the elements and the third one allows only digits after : or as part of the get expression.
If the whole string must match, add ^ at the start and $ at the end of the pattern.
Details:
key_in- - a substring
(?:get|(set)) - get or set (the latter is captured into Group 1)
\s* - zero or more whitespaces
{ - a { char
(?(1)\s*\w+\s*:) - a conditional construct: if Group 1 matched, match one or more word chars enclosed with zero or more whitespaces and then a colon
\s*\w+\s* - one or more word chars enclosed with zero or more whitespaces
}; - a literal substring.

In the pattern that you tried key_in-(get|set) { .* }; you are matching either get or set followed by { until the last occurrence of } which could possibly also match key_in-get { }; };
As an alternative solution, you could use an alternation | specifying each of the accepted parts for the get and the set.
key_in-(?:get\s*{\s*\w+|set\s*{\s*\w+\s*:\s*\w+)\s*};
The pattern matches
key_in- Match literally
(?: Non capture group
get\s*{\s*\w+ Match get, { between optional whitespace chars and 1+ word chars
| Or
set\s*{\s*\w+\s*:\s*\w+ Match set, { between optional whitespace chars and word chars on either side with : in between.
) Close non capture group
\s*}; Match optional whitespace chars and };
Regex demo

Regex - split by "_" and exclude file extension

I need to split the following string AAA_BBB_CCC.extension by "_" and exclude from the results any file extension.
Where A, B and C can be any character or space. I wish to get AAA, BBB and CCC.
I know that \.(?:.(?!\.))+$ will match .extension but I could not combine it with matching "_" for splitting.

Use the Path.GetFileNameWithoutExtension function to strip the extension from the file name.
Then use String.Split to get an array with three items:
var fileName = Path.GetFileNameWithoutExtension(fullName);
var parts = fileName.Split('_');
var partAAA = parts[0];
var partBBB = parts[1];
var partCCC = parts[2];
If the parts are always the same fixed number of characters long, you can as well extract them using the Substring function. No need to resort to regex here.

Another option is to make use of the .NET Group.Captures property and capture any char except an _ in a named capture group, which you can extract from the match using a named group.
^(?'val'[^_]+)(?:_(?'val'[^_]+))+\.\w+$
Explanation
^ Start of string
(?'val'[^_]+) Named group val, match 1+ chars other than _ using a negated character class
(?: Non caputure group
_(?'val'[^_]+) Match an _ and capture again 1+ chars other than _ in same named group val
)+ Close the non capture group and repeat 1+ times for at least 1 occurrence with _
\.\w+ Match a . and 1+ word chars
$ End of string
Regex demo
string pattern = #"^(?'val'[^_]+)(?:_(?'val'[^_]+))+\.\w+$";
string input = #"AAA_BBB_CCC.extension";
Match m = Regex.Match(input, pattern);
foreach (Capture capture in m.Groups["val"].Captures) {
Console.WriteLine(capture.Value);
}
Output
AAA
BBB
CCC

If you wanted to use a regex based approach here, you could try doing a find all on the following regex pattern:
[^_]+(?=.*\.\w+$)
This pattern will match every term in between underscore, except for the portion after the extension, which will be excluded by the lookahead.
Regex rx = new Regex(#"[^_]+(?=.*\.\w+$)");
string text = "AAA_BBB_CCC.extension";
MatchCollection matches = rx.Matches(text);
foreach (Match match in matches)
{
Console.WriteLine(match.Groups[0].Value);
}
This prints:
AAA
BBB
CCC

how to get password from string "password is Rtt3Ved36" by regexp?

on condition that string may be is "password Rtt3Ved36" (without "is").
(?<=password\ is|password\ ).*
That regexp doesn't work, because always return "is Rtt3Ved36" (but i need "Rtt3Ved36"). How to keep order in OR condition?

You may use
password(?: is)?\s*(.*)
and grab Group 1 value.
See the regex demo.
Details
password - a literal substring
(?: is)? - an optional substring space + is
\s* - 0+ whitespace
(.*) - Group 1: any 0+ chars other than a newline.
In C#:
var m = Regex.Match(s, #"password(?: is)?\s*(.*)");
var result = string.Empty;
if (m.Success)
{
result = m.Groups[1].Value;
}

According to this site: https://regex101.com/ your regex does work and returns "Rtt3Ved36".

Matching a pattern in a string

I have a string
string str = "I am fine. How are you? You need exactly 4 pieces of sandwiches. Your ADAST Count is 5. Okay thank you ";
What I want is, get the ADAST count value. For the above example, it is 5.
The problem here is, the is after the ADAST Count. It can be is or =. But there will the two words ADAST Count.
What I have tried is
var resultString = Regex.Match(str, #"ADAST\s+count\s+is\s+\d+", RegexOptions.IgnoreCase).Value;
var number = Regex.Match(resultString, #"\d+").Value;
How can I write the pattern which will search is or = ?

You may use
ADAST\s+count\s+(?:is|=)\s+(\d+)
See the regex demo
Note that (?:is|=) is a non-capturing group (i.e. it is used to only group alternations without pushing these submatches on to the capture stack for further retrieval) and | is an alternation operator.
Details:
ADAST - a literal string
\s+ - 1 or more whitespaces
count - a literal string
\s+ - 1 or more whitespaces
(?:is|=) - either is or =
\s+ - 1 or more whitespaces
(\d+) - Group 1 capturing one or more digits
C#:
var m = Regex.Match(s, #"ADAST\s+count\s+(?:is|=)\s+(\d+)", RegexOptions.IgnoreCase);
if (m.Success) {
Console.Write(m.Groups[1].Value);
}

Split string on whitespace ignoring parenthesis

I have a string such as this
(ed) (Karlsruhe Univ. (TH) (Germany, F.R.))
I need to split it into two such as this
ed
Karlsruhe Univ. (TH) (Germany, F.R.)
Basically, ignoring whitespace and parenthesis within a parenthesis
Is it possible to use a regex to achieve this?

If you can have more parentheses, it's better to use balancing groups:
string text = "(ed) (Karlsruhe Univ. (TH) (Germany, F.R.))";
var charSetOccurences = new Regex(#"\(((?:[^()]|(?<o>\()|(?<-o>\)))+(?(o)(?!)))\)");
var charSetMatches = charSetOccurences.Matches(text);
foreach (Match match in charSetMatches)
{
Console.WriteLine(match.Groups[1].Value);
}
ideone demo
Breakdown:
\(( # First '(' and begin capture
(?:
[^()] # Match all non-parens
|
(?<o> \( ) # Match '(', and capture into 'o'
|
(?<-o> \) ) # Match ')', and delete the 'o' capture
)+
(?(o)(?!)) # Fails if 'o' stack isn't empty
)\) # Close capture and last opening brace

\((.*?)\)\s*\((.*)\)
you will get the two values in two match groups \1 and \2
demo here : http://regex101.com/r/rP5kG2
and this is what you get if you search and replace with the pattern \1\n\2 which also seems to be what you need exactly

string str = "(ed) (Karlsruhe Univ. (TH) (Germany, F.R.))";
Regex re = new Regex(#"\((.*?)\)\s*\((.*)\)");
Match match = re.Match(str);

In general, No.
You can't describe recursive patterns in regular expression. ( Since it's not possible to recognize it with a finite automaton. )