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Using regex to split a formatted string to URL like StackOverFlow

I'm trying to write a parser that will create links found in posted text that are formatted like so:
[Site Description](http://www.stackoverflow.com)
to be rendered as a standard HTML link like this:
Site Description
So far what I have is the expression listed below and will work on the example above, but if will not work if the URL has anything after the ".com". Obviously there is no single regex expression that will find every URL but would like to be able to match as many as I can.
(\[)([A-Za-z0-9 -_]*)(\])(\()((http|https|ftp)\://[A-Za-z0-9\-\.]+\.[a-zA-Z]{2,3}(:[a-zA-Z0-9]*)?/?)(\))
Any help would be greatly appreciated. Thanks.

Darn. It seems #Jerry and #MikeH beat me to it. My answer is best, however, as the link tags are all uppercase ;)
Find what: \[([^]]+)\]\(([^)]+)\)
Replace with: $1
http://regex101.com/r/cY7lF0

Well, you could try negated classes so you don't have to worry about the parsing of the url itself?
\[([^]]+)\]\(([^)]+)\)
And replace with:
$1
regex101 demo
Or maybe use only the beginning parts to identify a url?
\[([^]]+)\]\(((?:https?|ftp)://[^)]+)\)
The replace is the same.

Deal with '#' through regex

Quick question , I have been trying to match any word containing a '#' from a string list and remove it, but I don't know how to handle it . been playing around on http://regexhero.net/tester/ trying but to no avail.
Essentially if it comes across #ff or wha#s up i will just regex.replace them.
any ideas on the Regular expression to use?.
Thanks.

Don't use regex - just use string.replace - it's a lot faster.

I have a previous answer that covers some hashtag matching approaches.
In summary, if you are pulling statuses containing hashtags from Twitter, you no longer need to find them yourself. You can now specify the include_entities parameter to have Twitter automatically call out mentions, links, and hashtags (if the method you are calling, like statuses/show supports this parameter.
If you just need the regular expression to locate the hashtags and capture it's elements, Twitter provides it in an open source library that contains the following pattern.
(^|[^0-9A-Z&/]+)(#|\uFF03)([0-9A-Z_]*[A-Z_]+[a-z0-9_\\u00c0-\\u00d6\\u00d8-\\u00f6\\u00f8-\\u00ff]*)
More detail and additional links are provided in the original answer.

So you're trying to remove any words containing a #?
If so, give this a try...
\w*#\w*
And replace with nothing, like so...
http://regexhero.net/tester/?id=cda1e713-bdab-4aa2-b63d-a87e9b2c9bce
apple# orange ban#ana becomes orange
But if you're simply trying to remove all instances of #, then String.Replace is the better choice. myString = myString.Replace("#", "");

Is it possible to use Regex to extract text from attributes repeated in a text file - c# .NET

I am working something at the moment and need to extract an attribute from a big list tags, they are formatted like this:
<appid="928" appname="extractapp" supportemail="me#mydomain.com" /><appid="928" appname="extractapp" supportemail="me#mydomain.com" />
The tags are repeated one after another and all have different appid, appname, supportemail.
I need to just extract all of the support emails, just the email address, without the supportemail=
Will I need to use two regex statements, one to seperate each individual tag, then loop through the result and pull out the emails?
I would then go through and Add the emails to a list, then loop through the list and write each one to a txt file, with a comma after it.
I've never really used Regex too much, so don't know if it's suitable for the above?
I would spend more time trying it myself but it's quite urgent. So hopefully somebody can help.

Have you considered Linq to XML?
http://www.hookedonlinq.com/LINQtoXML5MinuteOverview.ashx

Using XML is better, perhaps, but here's the regular expression you'd use (in case there's a particular reason you need/want to use regular expressions to read XML):
(appid="(?<AppID>[^"]+)" appname="(?<AppName>[^"]+)" supportemail="(?<SupportEmail>[^"]+)")
You can just take the last bit there for the support email but this will extract all of the attributes you mentioned and they will be "grouped" within each tag.

What about modify the string to have proper xml format and load xml to extract all the values of supportemail attribute?

Use
string pattern = "supportemail=\"([^\"]+)";
MatchCollection matches = Regex.Matches(inputString, pattern);
foreach(Match m in matches)
Console.WriteLine(m.Groups[1].Value);
See it here.

Problems you'll encounter by using regular expressions instead of an XML DOM:
All of the example regexes posted thus far will fail in the extremely common case that the attribute values are delimited by single quotes.
Any regex that depends on the attributes appearing in a specific order (e.g. appId before appName) will fail in the event that attributes - whose ordering is insignificant to XML - appear in an order different from what the regex expects.
A DOM will resolve entity references for you and a regex will not; if you use regex, you must check the returned values for (at least) the XML character entitites &, &apos;, >, <, and ".
There's a well-known edge case where using regular expressions to parse XML and XHTML unleashes the Great Old Ones. This will complicate your task considerably, as you will be reduced to gibbering madness and then the Earth will be eaten.

Using C# regex to select text based on custom tags

I have a string in c# containing some data i need to extract based on certain conditions.
The string contains many tenders in the following form :
<TENDER> some words, don't know how many, may contain numbers and things like slashes (/) or whatever <DESCRIPTION> some more words and possibly other things like numbers or whatever describing the tender here </DESCRIPTION> some more words and possibly numbers and weird things </TENDER>
This string doesn't contain any nested <TENDER> tags, its flat. The <DESCRIPTION> tags occur only once within the <TENDER> tags.
I'm using : <TENDER>(.+?)</TENDER> as the regex to split up the tenders and it works fine. If this is wrong or stupid and you know a better way to write this please let me know as I have discovered I suck at regex.
My problem that I now need to only select a tender if its description contains any word in a list of keywords (lets say for now i want to select a tender only if it contains either "concrete" or"brick" in the description).
So far the regex I have come up with looks like this, but I don't know what to put in the middle. Also I have a vague suspicion that this might return me some false positives.
<TENDER>(.+?)<DESCRIPTION>have no idea what to do here</DESCRIPTION>(.+?)</TENDER>
If any of you regex guru's could point me in the right direction I would be most appreciative.

Use
<TENDER>([^<>]+?)<DESCRIPTION>[^<>]*?(brick|concrete)[^<>]*?</DESCRIPTION>([^<>]+?)</TENDER>
I am using [^<>] instead of . to avoid leaving the tags.

Use IgnorePatternWhiteSpace because I have commented the pattern. It does not affect the data processing...it allows one to break out patterns and comment.
string pattern = #"
(?<=<TENDER>) # Look Behind for TENDER
(?<TenderBefore>.*?) # Put the data into the TenderBefore Named Match Capture Group
(?:<DESCRIPTION>)
(?=.*brick|concrete) # Look ahead for the keywords
(?<Description>.*?) # Put the data into the Description NMCG
(?:</DESCRIPTION>)
(?<TenderAfter>.*?) # Put text into NMCG TenderAfter
(?=<\/TENDER>) # Tender Look ahead.";
After processing the matches, extract the data out of each match such as
string Tender = string.Format("{0}<DESCRIPTION>{1}</DESCRIPTION>{2}",
myMatch.Groups["TenderBefore"].Value,
myMatch.Groups["Description"].Value,
myMatch.Groups["TenderAfter"].Value);
HTH

Instead of regex, try using a proper DOM parsing library, such as the Html Agility Pack. It should work with any tags, even custom ones.

Regular expression to define format of backup filenames

In the application I am currently working on, I have an option to create automatic backups of a certain file on the hard disk. What I would like to do is offer the user the possibility to configure the name of the file and its extension.
For example, the backup filename could be something like : "backup_month_year_username.bak". I had the idea to save the format in the form of a regular expression. For the example above, the regexp would look like :
"^backup_(?<Month>\d{2})_(?<Year>\d{2})_(?<Username>\w).(?<extension>bak)$"
I thought about using regex because I will also have to browse through the directory of backuped files to delete those older than a certain date. The main trouble I have now is how to create a filename using the regex. In a way I should replace the tags with the information. I could do that using regex.replace and another regex, but I feel it's a big weird doing that and it might be a better way.
Thanks
[Edit] Maybe I wasn't really clear in the first go, but the idea is of course that the user (in this case an admin that will know regex syntax) will have the possibility to modify the form of the filename, that's all the idea behind it[/Edit]

... and if the regex changes, it is next to impossible to reconstruct a string from a given regex.
Edit:
Create some predefined "place-holders": %u could be the user's name, %y could be the year, etc.:
backup_%m_%y_%u.bak
and then simple replace the %? with their actual values.

It sounds like you're trying to use the regular expression to create the file name from a pattern which the user should be able to specify.
Regular expressions can - AFAIK - not be used to create output, but only to validate input, so you'd have the user specify two things:
a file name production pattern like Bart suggested
a validation pattern in form of a regular expression that helps you split the file names into their parts
EDIT
By the way, your sample regex contains an error: The "." is use for "any character", also \w only matches one word character, so I guess you meant to write
"^backup_(?<Month>\d{2})_(?<Year>\d{2})_(?<Username>\w+)\.(?<extension>bak)$"

If the filename is always in this form, there is no reason for a regex, as it's easier to process with string.Split ...

With Bart's solution it is easy enough to split (using string.Split) the generated file name using underscore as the delimiter, to get back the information.

Ok, I think I have found a way to use only the regex. As I am using groups to get the information, I will use another regular expression to match the regular expression and replace the groups with the value:
Regex rgx = new Regex("\(\?\<Month\>.+?\)");
rgx.Replace("^backup_(?<Month>\d{2})_(?<Year>\d{2})_(?<Username>\w+)\.(?<extension>bak)$"
, DateTime.Now.Month.ToString());
Ok, it's really a hack, but at least it works and I have only one pattern defined by the user. It might not work if the regex is too complex, but I think I can deal with that problem.
What do you think?