Develop Reference

Converting Notepad++ REGEX to .NET C#

Working with a pipe-delimited file. Currently, I use Notepad++ find and replace REGEX pattern ^(?:[^|]*\|){5}\K[^|]* that replaces all lines with an empty string between the 5th and 6th |. I'm trying to programmatically do this process, but .NET does not support \K. I've tried a few instances of the backward lookup, but I cannot seem to grasp it.
string[] lines = File.ReadAllLines(path);
foreach (string line in lines)
{
string line2 = null;
string finalLine = line;
string[] col = line.Split('|');
if (col[5] != null)
{
line2 = Regex.Replace(line, #"^(?:[^|]*\|){5}\K[^|]*", "");

\K is a "workaround" for regex grammars/engines that don't support anchoring against look-behind assertions.
.NET's regex grammar has look-behind assertions (using the syntax (?<=subexpression)), so use them:
Regex.Replace(line, #"(?<=^(?:[^|]*\|){5})[^|]*", "")
In the context of .NET, this pattern now describes:
(?<= # begin (positive) look-behind assertion
^ # match start of string
(?: # begin non-capturing group
[^|]*\| # match (optional) field value + delimiter
){5} # end of group, repeat 5 times
) # end of look-behind assertion
[^|]* # match any non-delimiters (will only occur where the lookbehind is satisfied)

No need using lookbehinds, use capturing groups and backreferences:
line2 = Regex.Replace(line, #"^((?:[^|]*\|){5})[^|]*", "$1");
See proof.
EXPLANATION
--------------------------------------------------------------------------------
^ the beginning of the string
--------------------------------------------------------------------------------
( group and capture to \1:
--------------------------------------------------------------------------------
(?: group, but do not capture (5 times):
--------------------------------------------------------------------------------
[^|]* any character except: '|' (0 or more
times (matching the most amount
possible))
--------------------------------------------------------------------------------
\| '|'
--------------------------------------------------------------------------------
){5} end of grouping
--------------------------------------------------------------------------------
) end of \1
--------------------------------------------------------------------------------
[^|]* any character except: '|' (0 or more times
(matching the most amount possible))

How to write a regular expression that captures tags in a comma-separated list?

Here is my input:
#
tag1, tag with space, !##%^, 🦄
I would like to match it with a regex and yield the following elements easily:
tag1
tag with space
!##%^
🦄
I know I could do it this way:
var match = Regex.Match(input, #"^#[\n](?<tags>[\S ]+)$");
// if match is a success
var tags = match.Groups["tags"].Value.Split(',').Select(x => x.Trim());
But that's cheating, as it involves messing around with C#. There must be a neat way to do this with a regex. Just must be... right? ;D
The question is: how to write a regular expression that would allow me to iterate through captures and extract tags, without the need of splitting and trimming?

This works (?ms)^\#\s+(?:\s*((?:(?!,|^\#\s+).)*?)\s*(?:,|$))+
It uses C#'s Capture Collection to find a variable amount of field data
in a single record.
You could extend the regex further to get all records at once.
Where each record contains its own variable amount of field data.
The regex has built-in trimming as well.
Expanded:
(?ms) # Inline modifiers: multi-line, dot-all
^ \# \s+ # Beginning of record
(?: # Quantified group, 1 or more times, get all fields of record at once
\s* # Trim leading wsp
( # (1 start), # Capture collector for variable fields
(?: # One char at a time, but not comma or begin of record
(?!
,
| ^ \# \s+
)
.
)*?
) # (1 end)
\s*
(?: , | $ ) # End of this field, comma or EOL
)+
C# code:
string sOL = #"
#
tag1, tag with space, !##%^, 🦄";
Regex RxOL = new Regex(#"(?ms)^\#\s+(?:\s*((?:(?!,|^\#\s+).)*?)\s*(?:,|$))+");
Match _mOL = RxOL.Match(sOL);
while (_mOL.Success)
{
CaptureCollection ccOL1 = _mOL.Groups[1].Captures;
Console.WriteLine("-------------------------");
for (int i = 0; i < ccOL1.Count; i++)
Console.WriteLine(" '{0}'", ccOL1[i].Value );
_mOL = _mOL.NextMatch();
}
Output:
-------------------------
'tag1'
'tag with space'
'!##%^'
'??'
''
Press any key to continue . . .

Nothing wrong with cheating ;]
string input = #"#
tag1, tag with space, !##%^, 🦄";
string[] tags = Array.ConvertAll(input.Split('\n').Last().Split(','), s => s.Trim());

You can pretty much make it without regex. Just split it like this:
var result = input.Split(new []{'\n','\r'}, StringSplitOptions.RemoveEmptyEntries).Skip(1).SelectMany(x=> x.Split(new []{','},StringSplitOptions.RemoveEmptyEntries).Select(y=> y.Trim()));

C# regular expression

Please give a suggestion here:
I try to do a regex in C#. Here is the text
E1A: pop(+)
call T
call E1
E1B: return
TA: call F
call T1
I want to split it like this:
1)
E1A: pop(+)
call T
call E1
2)
E1B: return
3)
TA: call F
call T1
I tought at lookbehind, but it's not working because of the .+
Here is what I hope to work but it doesn't:
"[A-Z0-9]+[:].+(?=([A-Z0-9]+[:]))"
Does anyone have a better ideea?
EDIT: The "E1A","E1B","TA" are changing. All it remains the same is that they are made by letter and numbers follow by ":"

Regex regexObj = new Regex(
#"^ # Start of line
[A-Z0-9]+: # Match identifier
(?: # Match...
(?!^[A-Z0-9]+:) # (unless it's the start of the next identifier)
. # ... any character,
)* # repeat as needed.",
RegexOptions.Singleline | RegexOptions.Multiline | RegexOptions.IgnorePatternWhitespace);
allMatchResults = regexObj.Matches(subjectString);
Now allMatchResults.Count will contain the number of matches in subjectString, and allMatchResults.Item[i] will contain the ith match.

What RegEx string will find the last (rightmost) group of digits in a string?

Looking for a regex string that will let me find the rightmost (if any) group of digits embedded in a string. We only care about contiguous digits. We don't care about sign, commas, decimals, etc. Those, if found should simply be treated as non-digits just like a letter.
This is for replacement/incrementing purposes so we also need to grab everything before and after the detected number so we can reconstruct the string after incrementing the value so we need a tokenized regex.
Here's examples of what we are looking for:
"abc123def456ghi" should identify the'456'
"abc123def456ghi789jkl" should identify the'789'
"abc123def" should identify the'123'
"123ghi" should identify the'123'
"abc123,456ghi" should identify the'456'
"abc-654def" should identify the'654'
"abcdef" shouldn't return any match
As an example of what we want, it would be something like starting with the name 'Item 4-1a', extracting out the '1' with everything before being the prefix and everything after being the suffix. Then using that, we can generate the values 'Item 4-2a', 'Item 4-3a' and 'Item 4-4a' in a code loop.
Now If I were looking for the first set, this would be easy. I'd just find the first contiguous block of 0 or more non-digits for the prefix, then the block of 1 or more contiguous digits for the number, then everything else to the end would be the suffix.
The issue I'm having is how to define the prefix as including all (if any) numbers except the last set. Everything I try for the prefix keeps swallowing that last set, even when I've tried anchoring it to the end by basically reversing the above.

How about:
^(.*?)(\d+)(\D*)$
then increment the second group and concat all 3.
Explanation:
^ : Begining of string
( : start of 1st capture group
.*? : any number of any char not greedy
) : end group
( : start of 2nd capture group
\d+ : one or more digits
) : end group
( : start of 3rd capture group
\D* : any number of non digit char
) : end group
$ : end of string
The first capture group will match all characters until the first digit of last group of digits before the end of the string.
or if you can use named group
^(?<prefix>.*?)(?<number>\d+)(?<suffix>\D*)$

Try next regex:
(\d+)(?!.*\d)
Explanation:
(\d+) # One or more digits.
(?!.*\d) # (zero-width) Negative look-ahead: Don't find any characters followed with a digit.
EDIT (OFFTOPIC of the question):: This answer is incorrect but this question has already been answered in other posts so to avoid delete this one I will use this same regex other way, for example in Perl could be used like this to get same result as in C# (increment last digit):
s/(\d+)(?!.*\d)/$1 + 1/e;

You can also try little bit simpler version:
(\d+)[^\d]*$

This should do it:
Regex regexObj = new Regex(#"
# Grab last set of digits, prefix and suffix.
^ # Anchor to start of string.
(.*) # $1: Stuff before last set of digits.
(?<!\d) # Anchor start of last set of digits.
(\d+) # $2: Last set of one or more digits.
(\D*) # $3: Zero or more trailing non digits.
$ # Anchor to end of string.
", RegexOptions.IgnorePatternWhitespace);

What about not using Regex. Here's code snippet (for console)
string[] myStringArray = new string[] { "abc123def456ghi", "abc123def456ghi789jkl", "abc123def", "123ghi", "abcdef","abc-654def" };
char[] numberSet = new char[] { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' };
char[] filterSet = new char[] {'a','b','c','d','e','f','g','h','i','j','k','l','m',
'n','o','p','q','r','s','t','u','v','w','x','y','z','-'};
foreach (string myString in myStringArray)
{
Console.WriteLine("your string - {0}",myString);
int index1 = myString.LastIndexOfAny(numberSet);
if (index1 == -1)
Console.WriteLine("no number");
else
{
string mySubString = myString.Substring(0,index1 + 1);
string prefix = myString.Substring(index1 + 1);
Console.WriteLine("prefix - {0}", prefix);
int index2 = mySubString.LastIndexOfAny(filterSet);
string suffix = myString.Substring(0, index2 + 1);
Console.WriteLine("suffix - {0}",suffix);
mySubString = mySubString.Substring(index2 + 1);
Console.WriteLine("number - {0}",mySubString);
Console.WriteLine("_________________");
}
}
Console.Read();

C# Regex Grouping

I have to write a function that will get a string and it will have 2 forms:
XX..X,YY..Y where XX..X are max 4 characters and YY..Y are max 26 characters(X and Y are digits or A or B)
XX..X where XX..X are max 8 characters (X is digit or A or B)
e.g. 12A,784B52 or 4453AB
How can i user Regex grouping to match this behavior?
Thanks.
p.s. sorry if this is to localized

You can use named captures for this:
Regex regexObj = new Regex(
#"\b # Match a word boundary
(?: # Either match
(?<X>[AB\d]{1,4}) # 1-4 characters --> group X
, # comma
(?<Y>[AB\d]{1,26}) # 1-26 characters --> group Y
| # or
(?<X>[AB\d]{1,8}) # 1-8 characters --> group X
) # End of alternation
\b # Match a word boundary",
RegexOptions.IgnorePatternWhitespace);
X = regexObj.Match(subjectString).Groups["X"].Value;
Y = regexObj.Match(subjectString).Groups["Y"].Value;
I don't know what happens if there is no group Y, perhaps you might need to wrap the last line in an if statement.