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Find pattern to solve regex in one step

I have a problem to find the pattern that solves the problem in onestep.
The string looks like this:
Text1
Text1$Text2$Text3
Text1$Text2$Text3$Text4$Text5$Text6 etc.
What i want to get is: Take up to 4x Text. If there are more than "4xText" take only the last sign.
Example:
Text1$Text2$Text3$Text4$Text5$Text6 -> Text1$Text2$Text3$Text4&56
My current solution is:
First pattern:
^([^\$]*)\$?([^\$]*)\$?([^\$]*)\$?([^\$]*)\$?
After this i will do a substitution with the first pattern
New string: Text5$Text6
second pattern is:
([^\$])\b
result: 56
combine both and get the result:
Text1$Text2$Text3$Text4$56
For me it is not clear why i cant easily put the second pattern after the first pattern into one pattern. Is there something like an anchor that tells the engine to start the pattern from here like it would do if is would be the only pattern ?

You might use an alternation with a positive lookbehind and then concatenate the matches.
(?<=^(?:[^$]+\$){0,3})[^$]+\$?|[^$](?=\$|$)
Explanation
(?<= Positive lookbehind, assert what is on the left is
^(?:[^$]+\$){0,3} Match 0-3 times any char except $ followed by an optional $
) Close lookbehind
[^$]+\$? Match 1+ times any char except $, then match an optional $
| Or
[^$] Match any char except $
(?=\$|$) Positive lookahead, assert what is directly to the right is either $ or the end of the string
.NET regex demo | C# demo
Example
string pattern = #"(?<=^(?:[^$]*\$){0,3})[^$]*\$?|[^$](?=\$|$)";
string[] strings = {
"Text1",
"Text1$Text2$Text3",
"Text1$Text2$Text3$Text4$Text5$Text6"
};
Regex regex = new Regex(pattern);
foreach (String s in strings) {
Console.WriteLine(string.Join("", from Match match in regex.Matches(s) select match.Value));
}
Output
Text1
Text1$Text2$Text3
Text1$Text2$Text3$Text4$56

I strongly believe regular expression isn't the way to do that. Mostly because of the readability.
You may consider using simple algorithm like this one to reach your goal:
using System;
public class Program
{
public static void Main()
{
var input = "Text1$Text2$Text3$Text4$Text5$Text6";
var parts = input.Split('$');
var result = "";
for(var i=0; i<parts.Length; i++){
result += (i <= 4 ? parts[i] + "$" : parts[i].Substring(4));
}
Console.WriteLine(result);
}
}
There are also linq alternatives :
using System;
using System.Linq;
public class Program
{
public static void Main()
{
var input = "Text1$Text2$Text3$Text4$Text5$Text6";
var parts = input.Split('$');
var first4 = parts.Take(4);
var remainings = parts.Skip(4);
var result2 = string.Join("$", first4) + "$" + string.Join("", remainings.Select( r=>r.Substring(4)));
Console.WriteLine(result2);
}
}
It has to be adjusted to the actual needs but the idea is there

Try this code:
var texts = new string[] {"Text1", "Text1$Text2$Text3", "Text1$Text2$Text3$Text4$Text5$Text6" };
var parsed = texts
.Select(s => Regex.Replace(s,
#"(Text\d{1,3}(?:\$Text\d{1,3}){0,3})((?:\$Text\d{1,3})*)",
(match) => match.Groups[1].Value +"$"+ match.Groups[2].Value.Replace("Text", "").Replace("$", "")
)).ToArray();
// parsed is now: string[3] { "Text1$", "Text1$Text2$Text3$", "Text1$Text2$Text3$Text4$56" }
Explanation:
solution uses regex pattern: (Text\d{1,3}(?:\$Text\d{1,3}){0,3})((?:\$Text\d{1,3})*)
(...) - first capturing group
(?:...) - non-capturing group
Text\d{1,3}(?:\$Text\d{1,3} - match Text literally, then match \d{1,3}, which is 1 up to three digits, \$ matches $ literally
Rest is just repetition of it. Basically, first group captures first four pieces, second group captures the rest, if any.
We also use MatchEvaluator here which is delegate type defined as:
public delegate string MatchEvaluator(Match match);
We define such method:
(match) => match.Groups[1].Value +"$"+ match.Groups[2].Value.Replace("Text", "").Replace("$", "")
We use it to evaluate match, so takee first capturing group and concatenate with second, removing unnecessary text.

It's not clear to me whether your goal can be achieved using exclusively regex. If nothing else, the fact that you want to introduce a new character '&' into the output adds to the challenge, since just plain matching would never be able to accomplish that. Possibly using the Replace() method? I'm not sure that would work though...using only a replacement pattern and not a MatchEvaluator, I don't see a way to recognize but still exclude the "$Text" portion from the fifth instance and later.
But, if you are willing to mix regex with a small amount of post-processing, you can definitely do it:
static readonly Regex regex1 = new Regex(#"(Text\d(?:\$Text\d){0,3})(?:\$Text(\d))*", RegexOptions.Compiled);
static void Main(string[] args)
{
for (int i = 1; i <= 6; i++)
{
string text = string.Join("$", Enumerable.Range(1, i).Select(j => $"Text{j}"));
WriteLine(KeepFour(text));
}
}
private static string KeepFour(string text)
{
Match match = regex1.Match(text);
if (!match.Success)
{
return "[NO MATCH]";
}
StringBuilder result = new StringBuilder();
result.Append(match.Groups[1].Value);
if (match.Groups[2].Captures.Count > 0)
{
result.Append("&");
// Have to iterate (join), because we don't want the whole match,
// just the captured text.
result.Append(JoinCaptures(match.Groups[2]));
}
return result.ToString();
}
private static string JoinCaptures(Group group)
{
return string.Join("", group.Captures.Cast<Capture>().Select(c => c.Value));
}
The above breaks your requirement into three different capture groups in a regex. Then it extracts the captured text, composing the result based on the results.

Regex within a regex?

Truth is, I'm having a hard time writing a regex string to parse something in the form of
[[[tab name=dog content=cat|tab name=dog2 content=cat2]]]
This regex would be parsed so that I can dynamically build tabs as demonstrated here. Initially I tried a regex pattern like \[\[\[tab name=(?'name'.*?) content=(?'content'.*?)\]\]\]
But I realized I couldn't get the tab as a whole and build upon a query without doing a regex.replace. Is it possible to take the entire tab leading up to the pipe symbol as a group and then parse that group down from the sub key/value pairs?
This is the current regex string I'm working with \[\[\[(?'tab'tab name=(?'name'.*?) content=(?'content'.*?))\]\]\]
And here is my code for performing the regex. Any guidance would be appreciated.
public override string BeforeParse(string markupText)
{
if (CompiledRegex.IsMatch(markupText))
{
// Replaces the [[[code lang=sql|xxx]]]
// with the HTML tags (surrounded with {{{roadkillinternal}}.
// As the code is HTML encoded, it doesn't get butchered by the HTML cleaner.
MatchCollection matches = CompiledRegex.Matches(markupText);
foreach (Match match in matches)
{
string tabname = match.Groups["name"].Value;
string tabcontent = HttpUtility.HtmlEncode(match.Groups["content"].Value);
markupText = markupText.Replace(match.Groups["content"].Value, tabcontent);
markupText = Regex.Replace(markupText, RegexString, ReplacementPattern, CompiledRegex.Options);
}
}
return markupText;
}

Is this what you want?
string input = "[[[tab name=dog content=cat|tab name=dog2 content=cat2]]]";
Regex r = new Regex(#"tab name=([a-z0-9]+) content=([a-z0-9]+)(\||])");
foreach (Match m in r.Matches(input))
{
Console.WriteLine("{0} : {1}", m.Groups[1].Value, m.Groups[2].Value);
}
http://regexr.com/3boot

Maybe string.split will be better in that case? For example something like that :
strgin str = "[[[tab name=dog content=cat|tab name=dog2 content=cat2]]]";
foreach(var entry in str.Split('|')){
var eqBlocks = entry.Split('=');
var tabName = eqBlocks[1].TrimEnd(" content");
var content = eqBlocks[2];
}
Ugly code, but should work.

Try this:
Starts with a word boundary and followed only by allowed characters.
/\b[\w =]*/g
https://regex101.com/r/cI7jS7/1

Just distill the regex pattern down to the individual tab patterns such as name=??? content=??? and match that only. That pattern which will make each Match (two in you example) where the data can be extracted.
string text = #"[[[tab name=dog content=cat|tab name=dog2 content=cat2]]]";
string pattern = #"name=(?<Name>[^\s]+)\scontent=(?<Content>[^\s|\]]+)";
var result = Regex.Matches(text, pattern)
.OfType<Match>()
.Select(mt => new
{
Name = mt.Groups["Name"].Value,
Content = mt.Groups["Content"].Value,
});
The result is an enumerable list with the created dynamic entities with the tabs needed which can be directly bound to the control:
Note in the set notation [^\s|\]] the pipe | is treated as a literal in the set and not used as an or. The bracket ] does have to be escaped though to be treated as a literal. Finally the logic the parse will look for: "To not (^) be a space or a pipe or a brace for that set".

Replace all alphanumeric characters in a string except pattern

I'm trying to obfuscate a string, but need to preserve a couple patterns. Basically, all alphanumeric characters need to be replaced with a single character (say 'X'), but the following (example) patterns need to be preserved (note that each pattern has a single space at the beginning)
QQQ"
RRR"
I've looked through a few samples on negative lookahead/behinds, but still not haven't any luck with this (only testing QQQ).
var test = #"""SOME TEXT AB123 12XYZ QQQ""""empty""""empty""1A2BCDEF";
var regex = new Regex(#"((?!QQQ)(?<!\sQ{1,3}))[0-9a-zA-Z]");
var result = regex.Replace(test, "X");
The correct result should be:
"XXXX XXXX XXXXX XXXXX QQQ""XXXXX""XXXXX"XXXXXXXX
This works for an exact match, but will fail with something like ' QQR"', which returns
"XXXX XXXX XXXXX XXXXX XQR""XXXXX""XXXXX"XXXXXXXX

You can use this:
var regex = new Regex(#"((?> QQQ|[^A-Za-z0-9]+)*)[A-Za-z0-9]");
var result = regex.Replace(test, "$1X");
The idea is to match all that must be preserved first and to put it in a capturing group.
Since the target characters are always preceded by zero or more things that must be preserved, you only need to write this capturing group before [A-Za-z0-9]

Here's a non-regex solution. Works quite nice, althought it fails when there is one pattern in an input sequence more then once. It would need a better algorithm fetching occurances. You can compare it with a regex solution for a large strings.
public static string ReplaceWithPatterns(this string input, IEnumerable<string> patterns, char replacement)
{
var patternsPositions = patterns.Select(p =>
new { Pattern = p, Index = input.IndexOf(p) })
.Where(i => i.Index > 0);
var result = new string(replacement, input.Length);
if (!patternsPositions.Any()) // no pattern in the input
return result;
foreach(var p in patternsPositions)
result = result.Insert(p.Index, p.Pattern); // return patterns back
return result;
}

string placeholder and regular expressions

I have created a method where I can search for string placeholders, this I do with Regular expressions.
At the moment I try to expand this method by adding grouping features.
For example if I have this string:
"Hallo {g:test1} asdasd {p:test1} sdfsdf{o:test1}"
I want to :
Search for the string test1, even if there is standing a letter:(like g:) before it.
I want to search for: all strings with for example a g: before it.
I can't really figure out how to do this in C# can someone help me?
At the moment I programmed this:
private string test() {
string pattern = #"\{(.*?)\}";
string query = "Hallo {g:test1} asdasd {p:test1} sdfsdf{o:test1}";
var matches = Regex.Matches(query, pattern);
foreach (Match m in matches) {
Test = m.Groups[1].Value;
}
return Test;
}

Try this:
\{(?:.:)?(.*?)\}
It will match the text not including the letter and the colon which may be before it.
To limit this to strings with a particular letter before it:
\{(?:#:)(.*?)\} replacing # with the letter you are filtering on
e.g.
\{(?:g:)(.*?)\}

\{.:test1\}
\{g:.+?\}

How can I find a string after a specific string/character using regex

I am hopeless with regex (c#) so I would appreciate some help:
Basicaly I need to parse a text and I need to find the following information inside the text:
Sample text:
KeywordB:***TextToFind* the rest is not relevant but **KeywordB: Text ToFindB and then some more text.
I need to find the word(s) after a certain keyword which may end with a “:”.
[UPDATE]
Thanks Andrew and Alan: Sorry for reopening the question but there is quite an important thing missing in that regex. As I wrote in my last comment, Is it possible to have a variable (how many words to look for, depending on the keyword) as part of the regex?
Or: I could have a different regex for each keyword (will only be a hand full). But still don't know how to have the "words to look for" constant inside the regex

The basic regex is this:
var pattern = #"KeywordB:\s*(\w*)";
\s* = any number of spaces
\w* = 0 or more word characters (non-space, basically)
() = make a group, so you can extract the part that matched
var pattern = #"KeywordB:\s*(\w*)";
var test = #"KeywordB: TextToFind";
var match = Regex.Match(test, pattern);
if (match.Success) {
Console.Write("Value found = {0}", match.Groups[1]);
}
If you have more than one of these on a line, you can use this:
var test = #"KeywordB: TextToFind KeyWordF: MoreText";
var matches = Regex.Matches(test, #"(?:\s*(?<key>\w*):\s?(?<value>\w*))");
foreach (Match f in matches ) {
Console.WriteLine("Keyword '{0}' = '{1}'", f.Groups["key"], f.Groups["value"]);
}
Also, check out the regex designer here: http://www.radsoftware.com.au/. It is free, and I use it constantly. It works great to prototype expressions. You need to rearrange the UI for basic work, but after that it's easy.
(fyi) The "#" before strings means that \ no longer means something special, so you can type #"c:\fun.txt" instead of "c:\fun.txt"

Let me know if I should delete the old post, but perhaps someone wants to read it.
The way to do a "words to look for" inside the regex is like this:
regex = #"(Key1|Key2|Key3|LastName|FirstName|Etc):"
What you are doing probably isn't worth the effort in a regex, though it can probably be done the way you want (still not 100% clear on requirements, though). It involves looking ahead to the next match, and stopping at that point.
Here is a re-write as a regex + regular functional code that should do the trick. It doesn't care about spaces, so if you ask for "Key2" like below, it will separate it from the value.
string[] keys = {"Key1", "Key2", "Key3"};
string source = "Key1:Value1Key2: ValueAnd A: To Test Key3: Something";
FindKeys(keys, source);
private void FindKeys(IEnumerable<string> keywords, string source) {
var found = new Dictionary<string, string>(10);
var keys = string.Join("|", keywords.ToArray());
var matches = Regex.Matches(source, #"(?<key>" + keys + "):",
RegexOptions.IgnoreCase);
foreach (Match m in matches) {
var key = m.Groups["key"].ToString();
var start = m.Index + m.Length;
var nx = m.NextMatch();
var end = (nx.Success ? nx.Index : source.Length);
found.Add(key, source.Substring(start, end - start));
}
foreach (var n in found) {
Console.WriteLine("Key={0}, Value={1}", n.Key, n.Value);
}
}
And the output from this is:
Key=Key1, Value=Value1
Key=Key2, Value= ValueAnd A: To Test
Key=Key3, Value= Something

/KeywordB\: (\w)/
This matches any word that comes after your keyword. As you didn´t mentioned any terminator, I assumed that you wanted only the word next to the keyword.