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Simplify Regex grouping

var pattern = (?:[P|p]rint\("")(.+)(?:""\);?)
var input = Print("Hello World");
Results in two groups, the second one captures exactly what I want to capture and the first one is completely useless, how do I remove the first one?
I tried (?:ABC) it didn't work

Your pattern uses 1 capturing group () and 2 non capturing groups using (?:)
Those 2 non capturing groups you can omit as well as the | from the character class. I think you also would like to make the .* non greedy like .*? to prevent overmatching.
Then your pattern could look like(Matching an optional semicolon at the end):
[Pp]rint\("(.+?)"\);?
Regex demo
You might also use a version with a negated character class to match not a double quote:
[Pp]rint\(("[^"]+)"\);
Regex demo

Try following :
string input = "var input = Print(\"Hello World\");";
string pattern = "[Pp]rint\\(\"(?'message'[^\"]+)";
Match match = Regex.Match(input, pattern);
string message = match.Groups["message"].Value;

RegEx ignoring part of string to extract out text

I have the following string:
#delimabc#delim#delim123#delim#delim456#delim
and I need to write a .Net RegEx that finds 3 matches in this example (but assume the number of matches will be variable:
abc
123
456
How can I write a RegEx so that the expression only matches the first and second #delim, and then the third and fourth and so on?
The following will of course capture from the first to the last instance of the #delim string.
#delim(.+)+#delim

You could use look behind like:
(?<=#delim)\w+
(?<=#delim) is using a Positive Lookbehind which will match the characters #delim literally (case sensitive)
while \w+ will match any word character from [a-zA-Z0-9_]. To include or exclude characters you could replace \w by [a-zA-Z0-9_] and include the new characters or remove those that should not be evaluated in your expression.
Online Demo
Here is .NET Online Demo:
.NET Online Demo
VB.NET version
Dim sampleInput="#delimabc#delim#delim123#delim#delim456#delim"
Dim results = Regex.Matches(sampleInput,"(?<=#delim)\w+")
For Each item As Group In results
Console.WriteLine("Line: {0}", item)
Next
C# Version
var sampleInput = "#delimabc#delim#delim123#delim#delim456#delim";
var results = Regex.Matches(sampleInput, "(?<=#delim)\\w+");
foreach (Group item in results) {
Console.WriteLine("Line: {0}", item);
}
Updated version:
(?<=#delim)[^#].+?(?=#delim|$)

#delim(.+?)#delim
Try this .Set g flag.Just modifed your regex to add ?.Grab the caotures.See demo.
http://regex101.com/r/uH3tP3/1

You can use split on this regex:
(?:#delim)+
RegEx Demo
Alternatively replace given regex pattern by an empty string.

REGEX help needed in c#

I am very new to reg-ex and i am not sure whats going on with this one.... however my friend gave me this to solve my issue BUT somehow it is not working....
string: department_name:womens AND item_type_keyword:base-layer-underwear
reg-ex: (department_name:([\\w-]+))?(item_type_keyword:([\\w-]+))?
desired output: array OR group
1st element should be: department_name:womens
2nd should be: womens
3rd: item_type_keyword:base-layer-underwear
4th: base-layer-underwear
strings can contain department_name OR item_type_keyword, BUT not mendatory, in any order
C# Code
Regex regex = new Regex(#"(department_name:([\w-]+))?(item_type_keyword:([\w-]+))?");
Match match = regex.Match(query);
if (match.Success)
if (!String.IsNullOrEmpty(match.Groups[4].ToString()))
d1.ItemType = match.Groups[4].ToString();
this C# code only returns string array with 3 element
1: department_name:womens
2: department_name:womens
3: womens
somehow it is duplicating 1st and 2nd element, i dont know why. BUT its not return the other elements that i expect..
can someone help me please...
when i am testing the regex online, it looks fine to me...
http://fiddle.re/crvw1
Thanks

You can use something like this to get the output you have in your question:
string txt = "department_name:womens AND item_type_keyword:base-layer-underwear";
var reg = new Regex(#"(?:department_name|item_type_keyword):([\w-]+)", RegexOptions.IgnoreCase);
var ms = reg.Matches(txt);
ArrayList results = new ArrayList();
foreach (Match match in ms)
{
results.Add(match.Groups[0].Value);
results.Add(match.Groups[1].Value);
}
// results is your final array containing all results
foreach (string elem in results)
{
Console.WriteLine(elem);
}
Prints:
department_name:womens
womens
item_type_keyword:base-layer-underwear
base-layer-underwear
match.Groups[0].Value gives the part that matched the pattern, while match.Groups[1].Value will give the part captured in the pattern.
In your first expression, you have 2 capture groups; hence why you have twice department_name:womens appearing.
Once you get the different elements, you should be able to put them in an array/list for further processing. (Added this part in edit)
The loop then allows you to iterate over each of the matches, which you cannot exactly do with if and .Match() (which is better suited for a single match, while here I'm enabling multiple matches so the order they are matched doesn't matter, or the number of matches).
ideone demo
(?:
department_name # Match department_name
| # Or
item_type_keyword # Match item_type_keyword
)
:
([\w-]+) # Capture \w and - characters

It's better to use the alternation (or logical OR) operator | because we don't know the order of the input string.
(department_name:([\w-]+))|(item_type_keyword:([\w-]+))
DEMO
String input = #"department_name:womens AND item_type_keyword:base-layer-underwear";
Regex rgx = new Regex(#"(?:(department_name:([\w-]+))|(item_type_keyword:([\w-]+)))");
foreach (Match m in rgx.Matches(input))
{
Console.WriteLine(m.Groups[1].Value);
Console.WriteLine(m.Groups[2].Value);
Console.WriteLine(m.Groups[3].Value);
Console.WriteLine(m.Groups[4].Value);
}
IDEONE

Another idea using a lookahead for capturing and getting all groups in one match:
^(?!$)(?=.*(department_name:([\w-]+))|)(?=.*(item_type_keyword:([\w-]+))|)
as a .NET String
"^(?!$)(?=.*(department_name:([\\w-]+))|)(?=.*(item_type_keyword:([\\w-]+))|)"
test at regexplanet (click on .NET); test at regex101.com
(add m multiline modifier if multiline input: "^(?m)...)

If you use any spliting with And Or , etc that you can use
(department_name:(.*?)) AND (item_type_keyword:(.*?)$)
•1: department_name:womens
•2: womens
•3: item_type_keyword:base-layer-underwear
•4: base-layer-underwear

(?=(department_name:\w+)).*?:([\w-]+)|(?=(item_type_keyword:.*)$).*?:([\w-]+)
Try this.This uses a lookahead to capture then backtrack and again capture.See demo.
http://regex101.com/r/lS5tT3/52

C# RegEx - get only first match in string

I've got an input string that looks like this:
level=<device[195].level>&name=<device[195].name>
I want to create a RegEx that will parse out each of the <device> tags, for example, I'd expect two items to be matched from my input string: <device[195].level> and <device[195].name>.
So far I've had some luck with this pattern and code, but it always finds both of the device tags as a single match:
var pattern = "<device\\[[0-9]*\\]\\.\\S*>";
Regex rgx = new Regex(pattern);
var matches = rgx.Matches(httpData);
The result is that matches will contain a single result with the value <device[195].level>&name=<device[195].name>
I'm guessing there must be a way to 'terminate' the pattern, but I'm not sure what it is.

Use non-greedy quantifiers:
<device\[\d+\]\.\S+?>
Also, use verbatim strings for escaping regexes, it makes them much more readable:
var pattern = #"<device\[\d+\]\.\S+?>";
As a side note, I guess in your case using \w instead of \S would be more in line with what you intended, but I left the \S because I can't know that.

depends how much of the structure of the angle blocks you need to match, but you can do
"\\<device.+?\\>"

I want to create a RegEx that will parse out each of the <device> tags
I'd expect two items to be matched from my input string:
1. <device[195].level>
2. <device[195].name>
This should work. Get the matched group from index 1
(<device[^>]*>)
Live demo
String literals for use in programs:
#"(<device[^>]*>)"

Change your repetition operator and use \w instead of \S
var pattern = #"<device\[[0-9]+\]\.\w+>";
String s = #"level=<device[195].level>&name=<device[195].name>";
foreach (Match m in Regex.Matches(s, #"<device\[[0-9]+\]\.\w+>"))
Console.WriteLine(m.Value);
Output
<device[195].level>
<device[195].name>

Use named match groups and create a linq entity projection. There will be two matches, thus separating the individual items:
string data = "level=<device[195].level>&name=<device[195].name>";
string pattern = #"
(?<variable>[^=]+) # get the variable name
(?:=<device\[) # static '=<device'
(?<index>[^\]]+) # device number index
(?:]\.) # static ].
(?<sub>[^>]+) # Get the sub command
(?:>&?) # Match but don't capture the > and possible &
";
// Ignore pattern whitespace is to document the pattern, does not affect processing.
var items = Regex.Matches(data, pattern, RegexOptions.IgnorePatternWhitespace)
.OfType<Match>()
.Select (mt => new
{
Variable = mt.Groups["variable"].Value,
Index = mt.Groups["index"].Value,
Sub = mt.Groups["sub"].Value
})
.ToList();
items.ForEach(itm => Console.WriteLine ("{0}:{1}:{2}", itm.Variable, itm.Index, itm.Sub));
/* Output
level:195:level
name:195:name
*/

C# - Regex Match whole words

I need to match all the whole words containing a given a string.
string s = "ABC.MYTESTING
XYZ.YOUTESTED
ANY.TESTING";
Regex r = new Regex("(?<TM>[!\..]*TEST.*)", ...);
MatchCollection mc = r.Matches(s);
I need the result to be:
MYTESTING
YOUTESTED
TESTING
But I get:
TESTING
TESTED
.TESTING
How do I achieve this with Regular expressions.
Edit: Extended sample string.

If you were looking for all words including 'TEST', you should use
#"(?<TM>\w*TEST\w*)"
\w includes word characters and is short for [A-Za-z0-9_]

Keep it simple: why not just try \w*TEST\w* as the match pattern.

I get the results you are expecting with the following:
string s = #"ABC.MYTESTING
XYZ.YOUTESTED
ANY.TESTING";
var m = Regex.Matches(s, #"(\w*TEST\w*)", RegexOptions.IgnoreCase);

Try using \b. It's the regex flag for a non-word delimiter. If you wanted to match both words you could use:
/\b[a-z]+\b/i
BTW, .net doesn't need the surrounding /, and the i is just a case-insensitive match flag.
.NET Alternative:
var re = new Regex(#"\b[a-z]+\b", RegexOptions.IgnoreCase);

Using Groups I think you can achieve it.
string s = #"ABC.TESTING
XYZ.TESTED";
Regex r = new Regex(#"(?<TM>[!\..]*(?<test>TEST.*))", RegexOptions.Multiline);
var mc= r.Matches(s);
foreach (Match match in mc)
{
Console.WriteLine(match.Groups["test"]);
}
Works exactly like you want.
BTW, your regular expression pattern should be a verbatim string ( #"")

Regex r = new Regex(#"(?<TM>[^.]*TEST.*)", RegexOptions.IgnoreCase);
First, as #manojlds said, you should use verbatim strings for regexes whenever possible. Otherwise you'll have to use two backslashes in most of your regex escape sequences, not just one (e.g. [!\\..]*).
Second, if you want to match anything but a dot, that part of the regex should be [^.]*. ^ is the metacharacter that inverts the character class, not !, and . has no special meaning in that context, so it doesn't need to be escaped. But you should probably use \w* instead, or even [A-Z]*, depending on what exactly you mean by "word". [!\..] matches ! or ..
Regex r = new Regex(#"(?<TM>[A-Z]*TEST[A-Z]*)", RegexOptions.IgnoreCase);
That way you don't need to bother with word boundaries, though they don't hurt:
Regex r = new Regex(#"(?<TM>\b[A-Z]*TEST[A-Z]*\b)", RegexOptions.IgnoreCase);
Finally, if you're always taking the whole match anyway, you don't need to use a capturing group:
Regex r = new Regex(#"\b[A-Z]*TEST[A-Z]*\b", RegexOptions.IgnoreCase);
The matched text will be available via Match's Value property.