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How to use regex to find variable name beginning with # in a string expression?

The programmer hope to get two variables day1 and day2 by using regex, all the other variables in string expression beginning with the character # too.
The example of a string expression: #day1 - #day2 > 3
Thanks!

You can simply use positive lookahead here.
string = "#day1 - #day2 > 3";
Regex regex = new Regex("(?<=#)\\w+", RegexOptions.Compiled);
var match = regex.Matches(a);
foreach( var val in match )
{
Console.WriteLine(val);
}
val contains the match values.

You could use a lookbehind to get the variable names, like so:
var regex = new Regex("(?<=#)\\w+");
This will get the words preceded by an # sign

Regex match and replace operators in math operation

Given an input string
12/3
12*3/12
(12*54)/(3/4)
I need to find and replace each operator with a string that contains the operator
some12text/some3text
some12text*some2text/some12text
(some12text*some54text)/(some3text/some4text)
practical application:
From a backend (c#), i have the following string
34*157
which i need to translate to:
document.getElementById("34").value*document.getElementById("157").value
and returned to the screen which can be run in an eval() function.
So far I have
var pattern = #"\d+";
var input = "12/3;
Regex r = new Regex(pattern);
var matches = r.Matches(input);
foreach (Match match in matches)
{
// im at a loss what to match and replace here
}
Caution: i cannot do a blanket input.Replace() in the foreach loop, as it may incorrectly replace (12/123) - it should only match the first 12 to replace
Caution2: I can use string.Remove and string.Insert, but that mutates the string after the first match, so it throws off the calculation of the next match
Any pointers appreciated

Here you go
string pattern = #"\d+"; //machtes 1-n consecutive digits
var input = "(12*54)/(3/4)";
string result = Regex.Replace(input, pattern, "some$0Text");
$0 is the character group matching the pattern \d+. You can also write
string result = Regex.Replace(input, pattern, m => "some"+ m.Groups[0]+ "Text");
Fiddle: https://dotnetfiddle.net/JUknx2

Looking for patterns in a string how to?

I'm trying to find all instances of the substring EnemyType('XXXX') where XXXX is an arbitrary string and the instasnce of EnemyType('XXXX') can appear multiple times.
Right now I'm using a consortium of index of/substring functions in C# but would like to know if there's a cleaner way of doing it?

Use regex. Example:
using System.Text.RegularExpressions;
var inputString = " EnemyType('1234')abcdeEnemyType('5678')xyz";
var regex = new Regex(#"EnemyType\('\d{4}'\)");
var matches = regex.Matches(inputString);
foreach (Match i in matches)
{
Console.WriteLine(i.Value);
}
It will print:
EnemyType('1234')
EnemyType('5678')
The pattern to match is #"EnemyType\('\d{4}'\)", where \d{4} means 4 numeric characters (0-9). The parentheses are escaped with backslash.
Edit: Since you only want the string inside quotes, not the whole string, you can use named groups instead.
var inputString = " EnemyType('1234')abcdeEnemyType('5678')xyz";
var regex = new Regex(#"EnemyType\('(?<id>[^']+)'\)");
var matches = regex.Matches(inputString);
foreach (Match i in matches)
{
Console.WriteLine(i.Groups["id"].Value);
}
Now it prints:
1234
5678
Regex is a really nice tool for parsing strings. If you often parse strings, regex can make life so much easier.

c#: how to match a variable string followed by a space and currency and pull the currency?

I'm trying to match the following cases and pull the number value:
"b 30.00"
"bill 30.00"
"bill 30"
"b 30"
I've tried:
var regex = new Regex("^b(?-i:ill)?$ ^$?d+(.d{2})?$", RegexOptions.IgnoreCase);
However, this doesn't seem to return a match, and I'm not sure how to pull the digit.

You haven't well understand how to use anchors ^ & $, read about this.
var regex = new Regex(#"^[Bb](?:ill)? \d+(?:\.\d{2})?$");
or better since you only need ascii digits (and not all possible digits of the world):
var regex = new Regex(#"^[Bb](?:ill)? [0-9]+(?:\.[0-9]{2})?$");
If you want to figure a literal . you must escape it (same thing for a literal $). Note the use of a verbatim string to avoid double backslashes.
Feel free to add capture groups around what you want to capture.

You didn't mention if RegEx is actually required to accomplish your goal. If RegEx is not required, and you know that your string is in a specific format, you could just split the string:
string val = "bill 30.00";
string[] split = val.Split(' ');
string name = string.Empty;
decimal currency = 0m;
if (split.Length > 1)
{
name = split[0];
decimal.TryParse(split[1], out currency);
}

new Regex (#"\b\d+(.\d {2})*") should give you what you want

Just try the code
string Value = "bill 30.00";
string resultString = Regex.Match(Value, #"\d+").Value;

Search string using Pattern within long string in C#

I need to search for a pattern within a string.
For eg:
string big = "Hello there, I need information for ticket XYZ12345. I also submitted ticket ZYX54321. Please update.";
Now I need to extract/find/seek words based on the pattern XXX00000 i.e. 3 ALPHA and than 5 numeric.
Is there any way to do this ?
Even extraction will be okay for me.
Please help.

foreach (Match m in Regex.Matches(big, "([A-Za-z]{3}[0-9]{5})"))
{
if (m.Success)
{
m.Groups[1].Value // -- here is your match
}
}

How about this one?
([XYZ]{3}[0-9]{5})
You can use Regex Tester to test your expressions.

You can use simple regular expression to match your following string
([A-Za-z]{3}[0-9]{5})
the full code will be:
string strRegex = #"([A-Za-z]{3}[0-9]{5})";
Regex myRegex = new Regex(strRegex, RegexOptions.IgnoreCase);
string strTargetString = #"Hello there, I need information for ticket XYZ12345. I also submitted ticket ZYX54321. Please update.";
foreach (Match myMatch in myRegex.Matches(strTargetString))
{
if (myMatch.Success)
{
// Add your code here
}
}

You could always use a chatbot extension for the requests.
as for extracting the required information out of a sentence without any context
you can use regex for that.
you can use http://rubular.com/ to test it,
an example would be
...[0-9]
that would find XXX00000
hope that helped.

Use a regex:
string ticketNumber = string.Empty;
var match = Regex.Match(myString,#"[A-Za-z]{3}\d{5}");
if(match.Success)
{
ticketNumber = match.Value;
}

Here's a regex:
var str = "ABCD12345 ABC123456 ABC12345 XYZ98765";
foreach (Match m in Regex.Matches(str, #"(?<![A-Z])[A-Z]{3}[0-9]{5}(?![0-9])"))
Console.WriteLine(m.Value);
The extra bits are the zero-width negative look-behind ((?<![A-Z])) and look-ahead ((?![0-9])) expressions to make sure you don't capture extra numbers or letters. The above example only catches the third and fourth parts, but not the first and second. A simple [A-Z]{3}[0-9]{5} catches at least the specified number of characters, or more.