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Find hashtags in string

I am working on a Xamarin.Forms PCL project in C# and would like to detect all the hashtags.
I tried splitting at spaces and checking if the word begins with an # but the problem is if the post contains two spaces like "Hello #World Test" it would lose that the double space
string body = "Example string with a #hashtag in it";
string newbody = "";
foreach (var word in body.Split(' '))
{
if (word.StartsWith("#"))
newbody += "[" + word + "]";
newbody += word;
}
Goal output:
Example string with a [#hashtag] in it
I also only want it to have A-Z a-z 0-9 and _ stopping at any other character
Test #H3ll0_W0rld$%Test => Test [#H3ll0_W0rld]$%Test
Other Stack questions try to detect the string and extract it, I would like it work with it and put it back in the string without losing anything that methods such as splitting by certain characters would lose.

You can use Regex with #\w+ and $&
Explanation
# matches the character # literally (case sensitive)
\w+ matches any word character (equal to [a-zA-Z0-9_])
+ Quantifier — Matches between one and unlimited times, as many times as possible, giving back as needed (greedy)
$& Includes a copy of the entire match in the replacement string.
Example
var input = "asdads sdfdsf #burgers, #rabbits dsfsdfds #sdf #dfgdfg";
var regex = new Regex(#"#\w+");
var matches = regex.Matches(input);
foreach (var match in matches)
{
Console.WriteLine(match);
}
or
var result = regex.Replace(input, "[$&]" );
Console.WriteLine(result);
Ouput
#burgers
#rabbits
#sdf
#dfgdfg
asdads sdfdsf [#burgers], [#rabbits] dsfsdfds [#sdf] [#dfgdfg]
Updated Demo here
Another Example

Use a regular expression: \#\w*
string pattern = "\#\w*";
Regex rgx = new Regex(pattern, RegexOptions.IgnoreCase);
MatchCollection matches = rgx.Matches(input);

Regex printing newlines C#

I am using Regex to return two lines of text, but it returns newlines with additional text.
//Text is located in txt file and contains
I've been meaning to talk with you.
I've been meaning to talk with you.
I've been meaning to talk with you.
string text = File.ReadAllText(#"C:\...\1.txt");
Regex unit = new Regex(#"(?<Text>.+(\r\n){1}.+)");
MatchCollection mc = unit.Matches(text);
foreach (Match m in mc)
foreach (Group g in m.Groups)
Console.WriteLine(g.Value);

You may use
var m = Regex.Match(text, #"^.+(?:\n.+)?");
if (m.Success)
{
Console.Write(m.Value.Trim());
}
Details
^ - start of string
.+ - any 1+ chars other than an LF symbol
(?:\n.+)? - an optional sequence of:
\n - a newline
.+ - any 1+ chars other than an LF symbol
The .Trim() is used here to trim the result from a possible CR symbol (since in .NET regex, . also matches CR symbol.

How can i find and get the value of a match with regex?

I have the following pattern >4.66< I would like to find in a string. The following code is ment to find the pattern and give med the double value:
string data = File.ReadAllText("test.txt");
string pattern = "^>\\d.\\d<";
if (Regex.IsMatch(data, pattern))
{
MatchCollection mc = Regex.Matches(data, pattern);
foreach (Match m in mc)
{
double value = double.Parse(m.Value.Substring(1, m.Value.Length - 1));
string foo = "" + 2;
}
}
I think my pattern is wrong since i cant seem to find >4.66< and I see in the source that it is right there :D

Use the following regex:
(?<=>)\d+\.\d+(?=<)
Slightly simplified code:
string data = File.ReadAllText("test.txt");
MatchCollection mc = Regex.Matches(data, #"(?<=>)\d+\.\d+(?=<)");
foreach (Match m in mc)
{
double value = double.Parse(m.Value, CultureInfo.InvariantCulture);
}
You don't need to call IsMatch method, because Matches will simply return you empty collection if nothing is matched.

Main thing is, you are missing a quantifier. With \d you are matching exactly 1 digit. If you want to match more of them, you need to define it.
+ is a quantifier repeating the previous item 1 ore more.
To match a dot literally it needs to be escaped, because it is a special character in regex.
Use a verbatim string to avoid double escaping
Match only what you need (like Ulugbek described) with lookaround assertions or use a capturing group
I removed ^ from your pattern, because this is matching the start of the string, and you wrote you want to find within a string.
So we end up with:
string pattern = #">(\d.\d+)<";
MatchCollection mc = Regex.Matches(data, pattern);
foreach (Match m in mc)
{
double value = double.Parse(m.groups[1]);
}

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);
}

Regex help with sample pattern. C#

I decided to use Regex, now I have two problems :)
Given the input string "hello world [2] [200] [%8] [%1c] [%d]",
What would be an approprite pattern to match the instances of "[%8]" "[%1c]" + "[%d]" ? (So a percentage sign, followed by any length alphanumeric, all enclosed in square brackets).
for the "[2]" and [200], I already use
Regex.Matches(input, "(\\[)[0-9]*?\\]");
Which works fine.
Any help would be appreicated.

MatchCollection matches = null;
try {
Regex regexObj = new Regex(#"\[[%\w]+\]");
matches = regexObj.Matches(input);
if (matches.Count > 0) {
// Access individual matches using matches.Item[]
} else {
// Match attempt failed
}
} catch (ArgumentException ex) {
// Syntax error in the regular expression
}

The Regex needed to match this pattern of "[%anyLengthAlphaNumeric]" in a string is this "[(%\w+)]"
The leading "[" is escaped with the "\" then you are creating a grouping of characters with the (...). This grouping is defined as %\w+. The \w is a shortcut for all word characters including letters and digits no spaces. The + matches one or more instances of the previous symbol, character or group. Then the trailing "]" is escaped with a "\" and catches the closing bracket.
Here is a basic code example:
string input = #"hello world [2] [200] [%8] [%1c] [%d]";
Regex example = new Regex(#"\[(%\w+)\]");
MatchCollection matches = example.Matches(input);

Try this:
Regex.Matches(input, "\\[%[0-9a-f]+\\]");
Or as a combined regular expression:
Regex.Matches(input, "\\[(\\d+|%[0-9a-f]+)\\]");

How about #"\[%[0-9a-f]*?\]"?
string input = "hello world [2] [200] [%8] [%1c] [%d]";
MatchCollection matches = Regex.Matches(input, #"\[%[0-9a-f]*?\]");
matches.Count // = 3