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Edit Hyperlink in a PDF Using iTextSharp [duplicate]

Supposed I have the following string:
string str = "<tag>text</tag>";
And I would like to change 'tag' to 'newTag' so the result would be:
"<newTag>text</newTag>"
What is the best way to do it?
I tried to search for <[/]*tag> but then I don't know how to keep the optional [/] in my result...

Why use regex when you can do:
string newstr = str.Replace("tag", "newtag");
or
string newstr = str.Replace("<tag>","<newtag>").Replace("</tag>","</newtag>");
Edited to #RaYell's comment

To make it optional, simply add a "?" AFTER THE "/", LIKE THIS:
<[/?]*tag>

string str = "<tag>text</tag>";
string newValue = new XElement("newTag", XElement.Parse(str).Value).ToString();

Your most basic regex could read something like:
// find '<', find an optional '/', take all chars until the next '>' and call it
// tagname, then take '>'.
<(/?)(?<tagname>[^>]*)>
If you need to match every tag.
Or use positive lookahead like:
<(/?)(?=(tag|othertag))(?<tagname>[^>]*)>
if you only want tag and othertag tags.
Then iterate through all the matches:
string str = "<tag>hoi</tag><tag>second</tag><sometag>otherone</sometag>";
Regex matchTag = new Regex("<(/?)(?<tagname>[^>]*)>");
foreach (Match m in matchTag.Matches(str))
{
string tagname = m.Groups["tagname"].Value;
str = str.Replace(m.Value, m.Value.Replace(tagname, "new" + tagname));
}

var input = "<tag>text</tag>";
var result = Regex.Replace(input, "(</?).*?(>)", "$1newtag$2");

How to remove the exact occurence of characters from a string?

For Example, I have a string like :
string str = "santhosh,phani,ravi,phani123,praveen,sathish,prakash";
I want to delete the charaters ,phani from str.
Now, I am using str = str.Replace(",phani", string.Empty);
then my output is : str="santhosh,ravi123,praveen,sathish,prakash";
But I want a output like : str="santhosh,ravi,phani123,praveen,sathish,prakash";

string str = "santhosh,phani,ravi,phani123,praveen,sathish,prakash";
var words = str.Split(',');
str = String.Join(",", words.Where(word => word != "phani"));

the better choice is to use a Split and Join method.
Easy in Linq :
String str = "santhosh,phani,ravi,phani123,praveen,sathish,prakash";
String token = "phani";
String result = String.Join(",", str.Split(',').Where(s => s != token));
(edit : I take time for testing and i'm not first ^^)

String.join(",", str.split(',').ToList().remove("phani"));
Removes any given name from the list.

How about
str = str.Replace(",phani,", ",");
This, however, does not work if "phani" is the last item in the string. To get around this, you could do this:
string source = "...";
source += ","; // Explicitly add a comma to the end
source = source.Replace(",phani,", ",").TrimEnd(',');
This adds a comma, replaces "phani" and removes the trailing comma.
A third solution would be this:
str = String.Join(",", str.Split(',').ToList().Remove("phani").ToArray());

Try to use with comma instead of;
string str = "santhosh,ravi,phani,phani123,praveen,sathish,prakash";
str = str.Replace(",phani,", ",");
Console.WriteLine(str);
Output will be;
santhosh,ravi,phani123,praveen,sathish,prakash
Here is a DEMO.
As Davin mentioned in comment, this won't work if phani is last item in the string. Silvermind's answer looks like the right answer.

string str = "santhosh,phani,ravi,phani123,praveen,sathish,prakash";
string pattern = #"\b,phani,\b";
string replace = ",";
Console.WriteLine(Regex.Replace(str, pattern, replace));
Output:
santhosh,ravi,phani123,praveen,sathish,prakash

You may use the regular expression, but you have to take care of cases when your string starts or ends with the substring:
var pattern = #",?\bphani\b,?";
var regex = new Regex(pattern);
var result = regex.Replace(input, ",").Trim(',');
Shorter notation could look like this:
var result = Regex.Replace(input, #",?\bphani\b,?", ",").Trim(',');
Explanation of the regular expression: ,?\bphani\b,? matches the word phani, but only if preceded and followed by word-delimiter characters (because of the word boundary metacharacter \b), and it can be (but doesn't have to be) preceded and followed by the comma thanks to ,? which means none or more comma(s).
At the end we need to remove possible commas from the beginning and end of the string, that's why there's Trim(',') on the result.

String Replace Line Breaks

I have read an entire file into a string object :-
string result = File.ReadAllText(#"C:\TestLog.log");
I want to remove all line breaks, "\n", but i also need to preserve any instances in the string object where "\r\n" exists.
How can i do this?

It looks like you want a regular expression replace.
string result = File.ReadAllText(#"C:\TestLog.log");
string newresult = Regex.Replace(result, #"[^\\r]\\n", "");
So the pattern looks for any \n that is not preceded by \r.

result = result.Replace("\n","").Replace("\r","\r\n")
Without using regex though. Not sure if you intend to use that or not.

Regex to remove string from string

Is there a regex pattern that can remove .zip.ytu from the string below?
werfds_tyer.abc.zip.ytu_20111223170226_20111222.20111222

Here is an answer using regex as the OP asked.
To use regex, put the replacment text in a match ( ) and then replace that match with nothing string.Empty:
string text = #"werfds_tyer.abc.zip.ytu_20111223170226_20111222.20111222";
string pattern = #"(\.zip\.ytu)";
Console.WriteLine( Regex.Replace(text, pattern, string.Empty ));
// Outputs
// werfds_tyer.abc_20111223170226_20111222.20111222

Just use String.Replace()
String.Replace(".zip.ytu", "");
You don't need regex for exact matches.

txt = txt.Replace(".zip.ytu", "");
Why don't you simply do above?

Don't really know what is the ".zip.ytu", but if you don't need exact matches, you might use something like that:
string txt = "werfds_tyer.abc.zip.ytu_20111223170226_20111222.20111222";
Regex mRegex = new Regex(#"^([^.]*\.[^.]*)\.[^.]*\.[^_]*(_.*)$");
Match mMatch = mRegex.Match(txt);
string new_txt = mRegex.Replace(txt, mMatch.Groups[1].ToString() + mMatch.Groups[2].ToString());

use string.Replace:
txt = txt.Replace(".zip.ytu", "");

Here is the method I use for more complex repaces. Check out the link: http://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regex.replace(v=vs.110).aspx for a Regular Expression replace. I added the code below as well.
string input = "This is text with far too much " +
"whitespace.";
string pattern = "\\s+";
string replacement = " ";
Regex rgx = new Regex(pattern);
string result = rgx.Replace(input, replacement);
Console.WriteLine("Original String: {0}", input);
Console.WriteLine("Replacement String: {0}", result);

How do I replace part of a string in C#?

Supposed I have the following string:
string str = "<tag>text</tag>";
And I would like to change 'tag' to 'newTag' so the result would be:
"<newTag>text</newTag>"
What is the best way to do it?
I tried to search for <[/]*tag> but then I don't know how to keep the optional [/] in my result...

Why use regex when you can do:
string newstr = str.Replace("tag", "newtag");
or
string newstr = str.Replace("<tag>","<newtag>").Replace("</tag>","</newtag>");
Edited to #RaYell's comment

To make it optional, simply add a "?" AFTER THE "/", LIKE THIS:
<[/?]*tag>

string str = "<tag>text</tag>";
string newValue = new XElement("newTag", XElement.Parse(str).Value).ToString();

Your most basic regex could read something like:
// find '<', find an optional '/', take all chars until the next '>' and call it
// tagname, then take '>'.
<(/?)(?<tagname>[^>]*)>
If you need to match every tag.
Or use positive lookahead like:
<(/?)(?=(tag|othertag))(?<tagname>[^>]*)>
if you only want tag and othertag tags.
Then iterate through all the matches:
string str = "<tag>hoi</tag><tag>second</tag><sometag>otherone</sometag>";
Regex matchTag = new Regex("<(/?)(?<tagname>[^>]*)>");
foreach (Match m in matchTag.Matches(str))
{
string tagname = m.Groups["tagname"].Value;
str = str.Replace(m.Value, m.Value.Replace(tagname, "new" + tagname));
}

var input = "<tag>text</tag>";
var result = Regex.Replace(input, "(</?).*?(>)", "$1newtag$2");