C# Regex.Replace does not replace

Question

I've got a little problem for you geniuses.

I have tested a pattern with "RegexLab" for replacing/filtering text. It worked perfectly there, but my code didn't do well.

Pattern:

<li>(.*?)<ul>.*?</ul>

Replacement

<li>$1

Input:

<b>Title</b>\n<br/>\n<ul><li><b>Text</b>\n<ul><li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n</ul>\n</li>\n<li><b>Text</b>\n<ul><li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n</ul>\n</li>\n<li><b>Text</b>\n<ul><li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n</ul>\n</li>\n<li><b>Text</b>\n<ul><li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n</ul>\n</li>\n<li><b>Text</b>\n<ul><li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n</ul>\n</li>\n<li><b>Text</b>\n<ul><li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n</ul>\n</li>\n</ul>\n<b>Title</b><br/>\n<ul><li><b>Text</b>\n<ul><li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n</ul>\n</li>\n<li><b>Text</b>\n<ul><li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n</ul>\n</li>\n<li><b>Text</b>\n<ul><li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n</ul>\n</li>\n<li><b>Text</b>\n<ul><li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n</ul>\n</li>\n<li><b>Text</b>\n<ul><li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n</ul>\n</li>\n</ul>

What the output should be like:

<b>Title</b>\n<br/>\n<ul><li>Text\n</li>\n<li>Text\n</li>\n<li>Text\n</li>\n<li>Text\n</li>\n<li>Text\n</li>\n<li>Text\n</li>\n</ul>\n<b>Title</b><br/>\n<ul><li>Text\n</li>\n<li>Text\n</li>\n<li>Text\n</li>\n<li>Text\n</li>\n<li>Text\n</li>\n</ul>

My code:

string filteredText = Regex.Replace(Input, Pattern, Replacement);

Problem:

My output is wrong, I don't get the filtered text, I get the whole unfiltered Input. RegexLab shows me that everything is right.

Whole code (will look dirty here)

           string input = "<b>Title</b>\n<br/>\n<ul><li><b>Text</b>\n<ul><li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n</ul>\n</li>\n<li><b>Text</b>\n<ul><li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n</ul>\n</li>\n<li><b>Text</b>\n<ul><li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n</ul>\n</li>\n<li><b>Text</b>\n<ul><li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n</ul>\n</li>\n<li><b>Text</b>\n<ul><li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n</ul>\n</li>\n<li><b>Text</b>\n<ul><li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n</ul>\n</li>\n</ul>\n<b>Title</b><br/>\n<ul><li><b>Text</b>\n<ul><li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n</ul>\n</li>\n<li><b>Text</b>\n<ul><li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n</ul>\n</li>\n<li><b>Text</b>\n<ul><li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n</ul>\n</li>\n<li><b>Text</b>\n<ul><li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n</ul>\n</li>\n<li><b>Text</b>\n<ul><li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n<li>Trash</li>\n</ul>\n</li>\n</ul>";
        string pattern = @"<li>(.*?)<ul>.*?</ul>";
        string replacement = "<li>$1";
        string filteredText = Regex.Replace(input, pattern, replacement);

Working code in PHP (needed in C#):

preg_replace("/<li>(.*?)<ul>.*?<\/ul>/s",'<li>$1',$input);

I need a solution without HtmlAgilityPack!

Maybe it's time to switch to e.g. the HTML Agility Pack, rather than trying to mangle this all through regular expressions. — Damien_The_Unbeliever
– Damien_The_Unbeliever, Commented Feb 17, 2014 at 15:09
The pattern in your code sample doesn't match the one in your question. — BartoszKP
– BartoszKP, Commented Feb 17, 2014 at 15:12
@user3319473 have you checked the RegexOptions? Perhaps PHP has different default options than .NET. — James
– James, Commented Feb 17, 2014 at 15:17

Teejay · Accepted Answer · 2014-02-17 15:18:27Z

4

Try with:

Regex.Replace(input, pattern, replacement, RegexOptions.Singleline);

You need to have the interpreter to see to whole string as a single line text, otherwise . (dot) will not match the \n (line feed)

answered Feb 17, 2014 at 15:18

Teejay

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1 Comment

Wagner DosAnjos Over a year ago

Note that the SingleLine option is also specified on the original PHP regex with the /s switch at the end of the pattern. In .Net you could write it as (?s)<li>(.*?)<ul>.*?</ul> too. msdn.microsoft.com/en-us/library/az24scfc.aspx#options

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