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Why does my Regex.Replace string contain the replacement value twice?

I have the following string: aWesdE, which I want to convert to http://myserver.com/aWesdE.jpg using Regex.Replace(string, string, string, RegexOptions)
Currently, I use this code:
string input = "aWesdE";
string match = "(.*)";
string replacement = "http://myserver.com/$1.jpg";
string output = Regex.Replace(input, match, replacement,
RegexOptions.IgnoreCase | RegexOptions.Singleline);
The result is that output is ending up as: http://myserver.com/aWesdE.jpghttp://myserver.com/.jpg
So, the replacement value shows up correctly, and then appears to be appended again - very strange. What's going on here?

There are actually 2 matches in your Regex. You defined your match like this:
string match = "(.*)";
It means match zero or more characters, so you have 2 matches - empty string and your text. In order to fix it change the pattern to
string match = "(.+)";
It means match one or more characters - in that case you will only get a single match

Regex removing empty spaces when using replace

My situation is not about removing empty spaces, but keeping them. I have this string >[database values] which I would like to find. I created this RegEx to find it then go in and remove the >, [, ]. The code below takes a string that is from a document. The first pattern looks for anything that is surrounded by >[some stuff] it then goes in and "removes" >, [, ]
string decoded = "document in string format";
string pattern = #">\[[A-z, /, \s]*\]";
string pattern2 = #"[>, \[, \]]";
Regex rgx = new Regex(pattern);
Regex rgx2 = new Regex(pattern2);
foreach (Match match in rgx.Matches(decoded))
{
string replacedValue= rgx2.Replace(match.Value, "");
Console.WriteLine(match.Value);
Console.WriteLine(replacedValue);
What I am getting in first my Console.WriteLine is correct. So I would be getting things like >[123 sesame St]. But my second output shows that my replace removes not just the characters but the spaces so I would get something like this 123sesameSt. I don't see any space being replaced in my Regex. Am I forgetting something, perhaps it is implicitly in a replace?

The [A-z, /, \s] and [>, \[, \]] in your patterns are also looking for commas and spaces. Just list the characters without delimiting them, like this: [A-Za-z/\s]
string pattern = #">\[[A-Za-z/\s]*\]";
string pattern2 = #"[>,\[\]]";
Edit to include Casimir's tip.

After rereading your question (if I understand well) I realize that your two steps approach is useless. You only need one replacement using a capture group:
string pattern = #">\[([^]]*)]";
Regex rgx = new Regex(pattern);
string result = rgx.Replace(yourtext, "$1");
pattern details:
>\[ # literals: >[
( # open the capture group 1
[^]]* # all that is not a ]
) # close the capture group 1
] # literal ]
the replacement string refers to the capture group 1 with $1

By defining [>, \[, \]] in pattern2 you define a character group consisting of single characters like >, ,, , [ and every other character you listed in the square brackets. But I guess you don't want to match space and ,. So if you don't want to match them leave them out like
string pattern2 = #"[>\[\]]";
Alternatively, you could use
string pattern2 = #"(>\[|\])";
Thereby, you either match >[ or ] which better expresses your intention.

C# Regex for retrieving capital string in quotation mark

Given a string, I want to retrieve a string that is in between the quotation marks, and that is fully capitalized.
For example, if a string of
oqr"awr"q q"ASRQ" asd "qIKQWIR"
has been entered, the regex would only evaluate "ASRQ" as matching string.
What is the best way to approach this?
Edit: Forgot to mention the string takes a numeric input as well I.E: "IO8917AS" is a valid input

EDIT: If you actually want "one or more characters, and none of the characters is a lower-case letter" then you probably want:
Regex regex = new Regex("\"\\P{Ll}+\"");
That will then allow digits as well... and punctuation. If you want to allow digits and upper case letters but nothing else, you can use:
Regex regex = new Regex("\"[\\p{Lu}\\d]+\"");
Or in verbatim string literal form (makes the quotes more confusing, but the backslashes less so):
Regex regex = new Regex(#"""[\p{Lu}\d]+""");
Original answer (before digits were required)
Sounds like you just want (within the pattern)
"[A-Z]*"
So something like:
Regex regex = new Regex("\"[A-Z]*\"");
Or for full Unicode support, use the Lu Unicode character category:
Regex regex = new Regex("\"\\p{Lu}*\"");
EDIT: As noted, if you don't want to match an empty string in quotes (which is still "a string where everything is upper case") then use + instead of *, e.g.
Regex regex = new Regex("\"\\p{Lu}+\");
Short but complete example of finding and displaying the first match:
using System;
using System.Text.RegularExpressions;
class Program
{
public static void Main()
{
Regex regex = new Regex("\"\\p{Lu}+\"");
string text = "oqr\"awr\"q q\"ASRQ\" asd \"qIKQWIR\"";
Match match = regex.Match(text);
Console.WriteLine(match.Success); // True
Console.WriteLine(match.Value); // "ASRQ"
}
}

Like this:
"\"[A-Z]+\""
The outermost quotes are not part of the regex, they delimit a C# string.
This requires at least one uppercase character between quotes and works for the English language.

Please try the following:
[\w]*"([A-Z0-9]+)"

How to ignore regex matches in C#?

An input string:
string datar = "aag, afg, agg, arg";
I am trying to get matches: "aag" and "arg", but following won't work:
string regr = "a[a-z&&[^fg]]g";
string regr = "a[a-z[^fg]]g";
What is the correct way of ignoring regex matches in C#?

The obvious way is to use a[a-eh-z]g, but you could also try with a negative lookbehind like this :
string regr = "a[a-z](?<!f|g)g"
Explanation :
a Match the character "a"
[a-z] Match a single character in the range between "a" and "z"
(?<!XXX) Assert that it is impossible to match the regex below with the match ending at this position (negative lookbehind)
f|g Match the character "f" or match the character "g"
g Match the character "g"

Character classes aren't quite that fancy. The simple solution is:
a[a-eh-z]g
If you really want to explicitly list out the letters that don't belong, you could try something like:
a[^\W\d_A-Zfg]g
This character class matches everything except:
\W excludes non-word characters, i.e. punctuation, whitespace, and other special characters. What's left are letters, digits, and the underscore _.
\d removes digits so now we have letters and the underscore _.
_ removes the underscore so now we only match letters.
A-Z removes uppercase letters so now we only match lowercase letters.
Finally at this point we can list the individual lowercase letters we don't want to match.
All in all way more complicated than we'd likely ever want. That's regular expressions for ya!

What you're using is Java's set intersection syntax:
a[a-z&&[^fg]]g
..meaning the intersection of the two sets ('a' THROUGH 'z') and (ANYTHING EXCEPT 'f' OR 'g'). No other regex flavor that I know of uses that notation. The .NET flavor uses the simpler set subtraction syntax:
a[a-z-[fg]]g
...that is, the set ('a' THROUGH 'z') minus the set ('f', 'g').
Java demo:
String s = "aag, afg, agg, arg, a%g";
Matcher m = Pattern.compile("a[a-z&&[^fg]]g").matcher(s);
while (m.find())
{
System.out.println(m.group());
}
C# demo:
string s = #"aag, afg, agg, arg, a%g";
foreach (Match m in Regex.Matches(s, #"a[a-z-[fg]]g"))
{
Console.WriteLine(m.Value);
}
Output of both is
aag
arg

Try this if you want match arg and aag:
a[ar]g
If you want to match everything except afg and agg, you need this regex:
a[^fg]g

It seems like you're trying to match any three alphabetic characters, with the condition that the second character cannot be f or g. If this is the case, why not use the following regular expression:
string regr = "a[a-eh-z]g";

Regex: a[a-eh-z]g.
Then use Regex.Matches to get the matched substrings.

Regex pattern failing

I am trying to strip out all things that are in a string that are not a letter number or space so I created the regex
private static Regex _NonAlphaChars = new Regex("[^[A-Za-z0-9 ]]", RegexOptions.Compiled);
however When I call _NonAlphaChars.Replace("Scott,", ""); it returns "Scott,"
What am I doing wrong that it is not matching the ,?

private static Regex _NonAlphaChars =
new Regex("[^A-Za-z0-9 ]", RegexOptions.Compiled);

You did something funny with the double bracketing. Change it to just
[^A-Za-z0-9 ]
Dropping your original expression into The Regex Coach explained your regex as:
The regular expression is a sequence consisting of the expression '[[^A-Za-z0-9 ]' and the character ']'.
For contrast, the explanation of the alternative I wrote is:
The regular expression is a character class representing everything but the range of characters from the character 'A' to the character 'Z', the range of characters from the character 'a' to the character 'z', the range of characters from the character '0' to the character '9', and the character ' '.

Try this
[^A-Za-z0-9\s]
or
\W