Develop Reference

How to replace two first characters before underscore with regex?

I have example this string:
HU_husnummer
HU_Adrs
How can I replace HU? with MI?
So it will be MI_husnummer and MI_Adrs.
I am not very good at regex but I would like to solve it with regex.
EDIT:
The sample code I have now and that still does not work is:
string test = Regex.Replace("[HU_husnummer] int NOT NULL","^HU","MI");

Judging by your comments, you actually need
string test = Regex.Replace("[HU_husnummer] int NOT NULL",#"^\[HU","[MI");
Have a look at the demo
In case your input string really starts with HU, remove the \[ from the regex pattern.
The regex is #"^\[HU" (note the verbatim string literal notation used for regex pattern):
^ - matches the start of string
\[ - matches a literal [ (since it is a special regex metacharacter denoting a beginning of a character class)
HU - matches HU literally.

String varString="HU_husnummer ";
varString=varString.Replace("HU_","MI_");
Links
https://msdn.microsoft.com/en-us/library/system.string.replace(v=vs.110).aspx
http://www.dotnetperls.com/replace

using Substring
var abc = "HU_husnummer";
var result = "MI" + abc.Substring(2);
Replace in Regex.
string result = Regex.Replace(abc, "^HU", "MI");

Getting the substring after a character in C# using regex

I have the following input string:
string val = "[01/02/70]\nhello world ";
I want to get the all words after the last ] character.
Example output for a sample string above:
\nhello world

In C#, use Substring() with IndexOf:
string val = val.Substring(val.IndexOf(']') + 1);
If you have multiple ] symbols, and you want to get all the string after the last one, use LastIndexOf:
string val = "[01/02/70]\nhello [01/02/80] world ";
string val = val.Substring(val.LastIndexOf(']') + 1); // => " world "
If you are a fan of Regex, you might want to use a Regex.Replace like
string val = "[01/02/70]\nhello [01/02/80] world ";
val = Regex.Replace(val, #"^.*\]", string.Empty, RegexOptions.Singleline); // => " world "
See demo
Notes on REGEX:
RegexOptions.Singleline makes . match a linebreak
^ - matches beginning of string
.* - matches 0 or more characters but as many as possible (greedy matching)
\] - matches literal ] (as it is a special regex metacharacter, it must be escaped).

You need to use lookbehind assertion. And not only that, you have to enable DOTALL modifier also, so that it would also match the newline character present inbetween.
"(?s)(?<=\\]).*"
(?s) - DOTALL modifier.
(?<=\\]) - lookbehind which asserts that the match must be preceeded by a close bracket
.* - Matches any chracater zero or more times.
or
"(?s)(?<=\\])[\\s\\S]*"
Try this if you don't want to match the following newline character.
#"(?<=\][\n\r]*).*"

I think my regular expression pattern in C# is incorrect

I'm checking to see if my regular expression matches my string.
I have a filename that looks like somename_somthing.txt and I want to match it to somename_*.txt, but my code is failing when I try to pass something that should match. Here is my code.
string pattern = "somename_*.txt";
Regex r = new Regex(pattern, RegexOptions.IgnoreCase);
using (ZipFile zipFile = ZipFile.Read(fullPath))
{
foreach (ZipEntry e in zipFile)
{
Match m = r.Match("somename_something.txt");
if (!m.Success)
{
throw new FileNotFoundException("A filename with format: " + pattern + " not found.");
}
}
}

The asterisk is matching the underscore and throwing it off.
Try:
somename_(\w+).txt
The (\w+) here will match the group at this location.
You can see it match here: https://regex101.com/r/qS8wA5/1

In General
Regex give in this code matches the _ with an * meaning zero or more underscores instead of what you intended. The * is used to denote zero or more of the previous item. Instead try
^somename_(.*)\.txt$
This matches exactly the first part "somename_".
Then anything (.*)
And finally the end ".txt". The backslash escapes the 'dot'.
More Specific
You can also say if you only want letters and not numbers or symbols in the middle part of the match with:
^somename_[a-z]*\.txt$

As written, your regular expression
somename_*.txt
matches (in a case-insensitive manner):
the literal text somename, followed by
zero or more underscore characters (_), followed
any character (other than newline), followed
the literal text txt
And it will match that anywhere in the source text. You probably want to write something like
Regex myPattern = new Regex( #"
^ # anchor the match to start-of-text, followed by
somename # the literal 'somename', followed by
_ # a literal underscore character, followed by
.* # zero or of any character (except newline), followed by
\. # a literal period/fullstop, followed by
txt # the literal text 'txt'
$ # with the match anchored at end-of-text
" , RegexOptions.IgnoreCase|RegexOptions.IgnorePatternWhitespace
) ;

Hi I think the pattern should be
string pattern = "somename_.*\\.txt";
Regards

How to replace words following certain character and extract rest with REGEX

Assume that i have the following sentence
select PathSquares from tblPathFinding where RouteId=470
and StartingSquareId=267 and ExitSquareId=13
Now i want to replace words followed by = and get the rest of the sentence
Lets say i want to replace following word of = with %
Words are separated with space character
So this sentence would become
select PathSquares from tblPathFinding where RouteId=%
and StartingSquareId=% and ExitSquareId=%
With which regex i can achieve this ?
.net 4.5 C#

Use a lookbehind to match all the non-space or word chars which are just after to = symbol . Replacing the matched chars with % wiil give you the desired output.
#"(?<==)\S+"
OR
#"(?<==)\w+"
Replacement string:
%
DEMO
string str = #"select PathSquares from tblPathFinding where RouteId=470
and StartingSquareId=267 and ExitSquareId=13";
string result = Regex.Replace(str, #"(?<==)\S+", "%");
Console.WriteLine(result);
IDEONE
Explanation:
(?<==) Asserts that the match must be preceded by an = symbol.
\w+ If yes, then match the following one or more word characters.

RegEx.Replace to Replace Whole Words and Skip when Part of the Word

I am using regex to replace certain keywords from a string (or Stringbuilder) with the ones that I choose. However, I fail to build a valid regex pattern to replace only whole words.
For example, if I have InputString = "fox foxy" and want to replace "fox" with "dog" it the output would be "dog dogy".
What is the valid RegEx pattern to take only "fox" and leave "foxy"?
public string Replace(string KeywordToReplace, string Replacement) /
{
this.Replacement = Replacement;
this.KeywordToReplace = KeywordToReplace;
Regex RegExHelper = new Regex(KeywordToReplace, RegexOptions.IgnoreCase);
string Output = RegExHelper.Replace(InputString, Replacement);
return Output;
}
Thanks!

Regexes support a special escape sequence that represents a word boundary. Word-characters are everything in [a-zA-Z0-9]. So a word-boundary is between any character that belongs in this group and a character that doesn't. The escape sequence is \b:
\bfox\b

Do not forget to put '#' symbol before your '\bword\b'.
For example:
address = Regex.Replace(address, #"\bNE\b", "Northeast");
# symbol ensures escape character, backslash(\), does not get escaped!

You need to use boundary..
KeywordToReplace="\byourWord\b"