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Regex to disallow all symbols that windows doesnt allow in its file/folder names

The symbols not allowed in filename or folder name in windows are \ / : * ? " < > |. I wrote a regex for it but not able to write regex to exclude " (double quotes).
Regex regex = new Regex(#"^[\\\/\:\*\?\'\<\>\|]+$");
Tried as below but it didnt work:
Regex regex = new Regex(#"^[\\\/\:\*\?\'\<\>\|"]+$");
EDIT:
I am particularly looking for code with regex itself and hence its not a duplicate.
Help is greatly appreciated. Thanks.

Instead of using Regex you could do something like this:
var invalidChars = new HashSet<char>(Path.GetInvalidFileNameChars());
var invalid = input.Any(chr => invalidChars.Contains(chr));

#Allrameest answer using Path.GetInvalidFileNameChars() is probably the one you should use.
What I wanted to address is the fact that your regex is actually wrong or very ineffective (I don't know what exectly you wanted to do).
So, using:
var regex = new Regex(#"^[\\\/\:\*\?\'\<\>\|]+$");
mean you match a string which consists ONLY of "forbidden" characters (BTW, I think single quote ' is not invalid). Is it what you want? Don't think so. What you did is:
^ start of the string
[...]+ invalid characters only (at least once)
$ end of the string
Maybe you wanted #"^[^...]+$" (hat used twice)?
Anyway, solution for your problem (with regex) is:
don't use ^ or $ just try to find any of those and bomb out quickly
in raw string (the one starting with #") you escape double quotes by doubling it.
So, the right regex is:
var regex = new Regex(#"[\\\/\:\*\?\""\<\>\|]");
if (regex.Match(filename).Success) {
throw new ArgumentException("Bad filename");
}
Just find any and bomb out.
UPDATE by #JohnLBevan
var regex = new Regex(
"[" + Regex.Escape(new string(Path.GetInvalidFileNameChars())) + "]");
if (regex.Match(filename).Success) {
throw new ArgumentException("Bad filename");
}
(Not using string.Format(...) as this Regex should be static and precompiled anyway)

RegEx matching for a filename

I have no experience using regular expressions, and although I should spend some time training in them, I have a need for a simple one.
I want to find a match of P*.txt in a given string (meaning anything that starts with a P, followed by anything, and ending in ".txt".
eg:
string myString = "P671221.txt";
Regex reg = new Regex("P*.txt"); //<--- what goes here?
if (reg.IsMatch(myString)
{
Console.WriteLine("Match!"));
}
This example doesn't work because it will return a match for ".txt" or "x.txt" etc. How do I do this?

myString.StartsWith("P") && myString.EndsWith(".txt")
EDIT: Removed my regex

Updated:
string start + (p) + any characters + .txt + string end
^(?i:p).*\.txt$
A more precise alternative would be:
string start + (p) + [specific characters] + .txt + string end
( currently specified are: "a-z", "0-9", space, & underscore )
^(?i:p)(?i:[a-z0-9 _])*\.txt$
Live Demo
Original Solution
( quotes were included, as I overlooked that quotes are part of the code but not
the string )
preceding quotes + (p) + any characters + .txt + following quotes
(?<=")(?i:p).*\.txt(?=")
Image
Live Demo

P[\d]+\.txt this will work. If you have fix number of digits then you can do it like P[\d]{6}\.txt. Just replace the 6 with your desired fix number.
If the value in between the starting letter P and extension .txt can be alphanumeric use P[\w]+\.txt

string myString = "P671221.txt";
Regex reg = new Regex("P(.*?)\\.txt"); //--> if anything goes after P
if (reg.IsMatch(myString))
Console.WriteLine("Match!");

This should meet the requirements that you have presented.
c#
[Pp].*.(?:txt)+$

The best option to get files that start with P & end with .txt with regex is:
^P\w+\.txt$

Regex string issue in making plain text urls clickable

I need a working Regex code in C# that detects plain text urls (http/https/ftp/ftps) in a string and make them clickable by putting an anchor tag around it with same url. I have already made a Regex pattern and the code is attached below.
However, if there is already any clickable url is present in the input string then the above code puts another anchor tag over it. For example the existing substring in the below code: string sContent: "ftp://www.abc.com'>ftp://www.abc.com" has another anchor tag over it when the code below is run. Is there any way to fix it?
string sContent = "ttt <a href='ftp://www.abc.com'>ftp://www.abc.com</a> abc ftp://www.abc.com abbbbb http://www.abc2.com";
Regex regx = new Regex("(http|https|ftp|ftps)://([\\w+?\\.\\w+])+([a-zA-Z0-9\\~\\!\\#\\#\\$\\%\\^\\&\\*\\(\\)_\\-\\=\\+\\\\\\/\\?\\.\\:\\;\\'\\,]*)?", RegexOptions.IgnoreCase);
MatchCollection mactches = regx.Matches(sContent);
foreach (Match match in mactches)
{
sContent = sContent.Replace(match.Value, "<a href='" + match.Value + "'>" + match.Value + "</a>");
}
Also, I want a Regex code to make emails as clickable with "mailto" tag. I can do it myself but the above mentioned issue of double anchor tag will also appear in it.

I noticed in your example test string that if a duplicate link e.g. ftp://www.abc.com is in the string and is already linked then the result will be to double anchor that link. The Regular Expression that you already have and that #stema has supplied will work, but you need to approach how you replace the matches in the sContent variable differently.
The following code example should give you what you want:
string sContent = "ttt <a href='ftp://www.abc.com'>ftp://www.abc.com</a> abc ftp://www.abc.com abbbbb http://www.abc2.com";
Regex regx = new Regex("(?<!(?:href='|<a[^>]*>))(http|https|ftp|ftps)://([\\w+?\\.\\w+])+([a-zA-Z0-9\\~\\!\\#\\#\\$\\%\\^\\&\\*\\(\\)_\\-\\=\\+\\\\\\/\\?\\.\\:\\;\\'\\,]*)?", RegexOptions.IgnoreCase);
MatchCollection matches = regx.Matches(sContent);
for (int i = matches.Count - 1; i >= 0 ; i--)
{
string newURL = "<a href='" + matches[i].Value + "'>" + matches[i].Value + "</a>";
sContent = sContent.Remove(matches[i].Index, matches[i].Length).Insert(matches[i].Index, newURL);
}

Try this
Regex regx = new Regex("(?<!(?:href='|>))(http|https|ftp|ftps)://([\\w+?\\.\\w+])+([a-zA-Z0-9\\~\\!\\#\\#\\$\\%\\^\\&\\*\\(\\)_\\-\\=\\+\\\\\\/\\?\\.\\:\\;\\'\\,]*)?", RegexOptions.IgnoreCase);
It should work for your example.
(?<!(?:href='|>)) is a negative lookbehind, that means the pattern matches only if it is not preceeded by "href='" or ">".
See lookarounds on regular-expressions.info
and the especially the zero-width negative lookbehind assertion on msdn
See something similar on Regexr. I had to remove the alternation from the look behind, but .net should be able to handle it.
Update
To ensure that there are also (maybe possible) cases like "<p>ftp://www.def.com</p>" correctly handled, I improved the regex
Regex regx = new Regex("(?<!(?:href='|<a[^>]*>))(http|https|ftp|ftps)://([\\w+?\\.\\w+])+([a-zA-Z0-9\\~\\!\\#\\#\\$\\%\\^\\&\\*\\(\\)_\\-\\=\\+\\\\\\/\\?\\.\\:\\;\\'\\,]*)?", RegexOptions.IgnoreCase);
The lookbehind (?<!(?:href='|<a[^>]*>)) is now checking that there is not a "href='" nor a tag starting with "
The output of the teststring
ttt <a href='ftp://www.abc.com'>ftp://www.abc.com</a> abc <p>ftp://www.def.com</p> abbbbb http://www.ghi.com
is with this expression
ttt <a href='ftp://www.abc.com'>ftp://www.abc.com</a> abc <p><a href='ftp://www.def.com'>ftp://www.def.com</a></p> abbbbb <a href='http://www.ghi.com'>http://www.ghi.com</a>

I know I arrived late to this party, but there are several problems with the regex that the existing answers don't address. First and most annoying, there's that forest of backslashes. If you use C#'s verbatim strings, you don't have to do all that double escaping. And anyway, most of the backslashes weren't needed in the first place.
Second, there's this bit: ([\\w+?\\.\\w+])+. The square brackets form a character class, and everything inside them is treated either as a literal character or a class shorthand like \w. But getting rid of the square brackets isn't enough to make it work. I suspect this is what you were trying for: \w+(?:\.\w+)+.
Third, the quantifiers at the end of the regex - ]*)? - are mismatched. * can match zero or more characters, so there's no point making the enclosing group optional. Also, that kind of arrangement can result in severe performance degradation. See this page for details.
There are other, minor problems, but I won't go into them right now. Here's the new and improved regex:
#"(?n)(https?|ftps?)://\w+(\.\w+)+([-a-zA-Z0-9~!##$%^&*()_=+/?.:;',\\]*)(?![^<>]*+(>|</a>))"
The negative lookahead - (?![^<>]*+(>|</a>)) is what prevents matches inside tags or in the content of an anchor element. It's still very crude, though. There are several areas, like inside <script> elements, where you don't want it to match but it does. But trying to cover all the possibilities would result in a mile-long regex.

Check out: Detect email in text using regex and Regex URL Replace, ignore Images and existing Links, just replace the regex for links, it will never replace a link inside a tag, only in contents.
http://html-agility-pack.net/?z=codeplex
Something like:
string textToBeLinkified = "... your text here ...";
const string regex = #"((www\.|(http|https|ftp|news|file)+\:\/\/)[_.a-z0-9-]+\.[a-z0-9\/_:#=.+?,##%&~-]*[^.|\'|\# |!|\(|?|,| |>|<|;|\)])";
Regex urlExpression = new Regex(regex, RegexOptions.IgnoreCase | RegexOptions.ExplicitCapture);
HtmlAgilityPack.HtmlDocument doc = new HtmlAgilityPack.HtmlDocument();
doc.LoadHtml(textToBeLinkified);
var nodes = doc.DocumentNode.SelectNodes("//text()[not(ancestor::a)]") ?? new HtmlNodeCollection();
foreach (var node in nodes)
{
node.InnerHtml = urlExpression.Replace(node.InnerHtml, #"$0");
}
string linkifiedText = doc.DocumentNode.OuterHtml;

extract links regex c#

I've been trying to solve these problem for last two hours but seems like I can't find any solution.
I need to extract links from an HTML file. There are 100+ links, but only 25 of them are valid.
Valid links are placed inside
<td><a href=" (link) ">
First I had (and still have) a problem with double quotes inside verbatim strings. So, I have replaced verbatim with "normal" strings so I can use \" for " but the problem is that this Regex I have written doesn't work
Match LinksTemp = Regex.Match(
htmlCode,
"<td><a href=\"(.*)\">",
RegexOptions.IgnoreCase);
as I get "<td><a href="http://www.google.com"> as output instead of http://www.google.com
Anyone know how can I solve this problem and how can I use double quotes inside of verbatim strings (example #" <>"das"sa ")

Escaped double quotes sample: #"some""test"
Regex sample: "<a href=\"(.*?)\">"
var match = Regex.Match(html, "<td><a href=\"(.*?)\">",
RegexOptions.Singleline); //spelling error
var url = match.Groups[1].Value;
Also you may want to use Regex.Matches(...) instead of Regex.Match(...)

If you want to take every elements use code simply like this:
string htmlCode = "<td><a href=\" www.aa.pl \"><td> <a href=\" www.cos.com \"><td>";
Regex r = new Regex( "<a href=\"(.*?)\">", RegexOptions.IgnoreCase );
MatchCollection mc = r.Matches(htmlCode);
foreach ( Match m1 in mc ) {
MessageBox.Show( m1.Groups[1].ToString() );
}

Why not parse this with an HTML-parsing is good and fast HTML-Parsing.
example:
string HTML = "<td><a href='http://www.google.com'>";
HtmlDocument doc = new HtmlDocument();
doc.LoadHtml(HTML);
HtmlNodeCollection a = doc.DocumentNode.SelectNodes("//a[#href]");
string url = a[0].GetAttributeValue("href", null);
Console.WriteLine(url);
Console.ReadLine();
you need import using HtmlAgilityPack;

Get the number of an href url parameter from downloaded html page?

I am trying to get an ID from a url parameter inside an href that looks like this:
MyItemName
I want the 71312 only and at the momment I am trying to do it using regex (but if you have a better approch I would be glad to try):
string html,itemID;
using (var client = new WebClient())
{
html = client.DownloadString("http://www.mysite.com/search.php?search_text=" + myItemName);
}
string pattern = "" + myItemName + "";
Match m = Regex.Match(html, pattern, RegexOptions.IgnoreCase);
if (m.Success)
{
itemID = m.Groups[1].Value;
MessageBox.Show(itemID);
}
Example of the html:
more html body
<h1>Items - List</h1>
<p>MyItemNameTest, MyItemNameTestB, MYItemNameOther</p>
</div>
more html body

To show where your regex went wrong:
. and ? are special characters in regular expressions. . means "any character" and ? means "zero or one occurences of the previous expression". Therefore your regex fails to match. Also, you need to use verbatim strings in C# (unless you want to escape every backslash):
#"" + myItemName + "";
will probably work.
That said, unless all the links you're examining follow exactly this format, you might run into problems. It's kind of a running gag here on SO that parsing HTML with regular expressions will earn you the wrath of Cthulhu.

Use:
Uri u = new Uri("http://www.mysite.com/myitem.php?id=12313");
string s = u.Query;
HttpUtility.ParseQueryString(s).Get("id");
In variable id you have the number. Figure out the rest of the function :)