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How to validate Regex

Im having a hard time with grouping parts of a Regex. I want to validate a few things in a string that follows this format: I-XXXXXX.XX.XX.XX
Validate that the first set of 6 X's (I-xxxxxx.XX.XX.XX) does not contain characters and its length is no more than 6.
Validate that the third set of X's (I-XXXXXX.XX.xx.XX) does not contain characters and is only 1 or 2.
Now, I have already validation on the last set of XX's to make sure the numbers are 1-8 using
string pattern1 = #"^.+\.(0?[1-8])$";
Match match = Regex.Match(TxtWBS.Text, pattern1);
if (match.Success)
;
else
{ errMessage += "WBS invalid"; errMessage +=
Environment.NewLine; }
I just cant figure out how to target specific parts of the string. Any help would be greatly appreciated and thank you in advance!

You're having some trouble adding new validation to this string because it's very generic. Let's take a look at what you're doing:
^.+\.(0?[1-8])$
This finds the following:
^ the start of the string
.+ everything it can, other than a newline, basically jumping the engine's cursor to the end of your line
\. the last period in the string, because of the greedy quantifier in the .+ that comes before it
0? a zero, if it can
[1-8] a number between 1 and 8
()$ stores the two previous things in a group, and if the end of the string doesn't come after this, it may even backtrace and try the same thing from the second to last period instead, which we know isn't a great strategy.
This ends up matching a lot of weird stuff, like for example the string The number 0.1
Let's try patterning something more specific, if we can:
^I-(\d{6})\.(\d{2})\.(\d{1,2})\.([1-8]{2})$
This will match:
^I- an I and a hyphen at the start of the string
(\d{6}) six digits, which it stores in a capture group
\. a period. By now, if there was any other number of digits than six, the match fails instead of trying to backtrace all over the place.
(\d{2})\. Same thing, but two digits instead of six.
(\d{1,2})\. Same thing, the comma here meaning it can match between one and two digits.
([1-8]{2}) Two digits that are each between 1 and 8.
$ The end of the string.
I hope I understood what exactly you're trying to match here. Let me know if this isn't what you had in mind.

This regex:
^.-[0-9]{6}(\.[1-8]{1,2}){3}$
will validate the following:
The first character can be any character, but is of length 1
It is followed by a dash
The dash is followed by exactly 6 numbers 0 - 9. (If this could be less than 6 characters - for example, between 3 and 6 characters - just replace {6} with {3,6}).
This is followed by 3 groups of characters. Each of this groups are proceeded by a period, are of length 1 or 2, and can be any number 1 - 8.
An example of a valid string is:
I-587954.12.34.56
This is also valid:
I-587954.1.3.5
But this isn't:
I-587954.12.80.356
because the second-to-last group contains a 0, and because the last group is of length 3.
Pleas let me know if I have misunderstood any of the rules.

^I-([0-9]{1,6})\.(.{1,2})\.(0[1-2])\.(.{1,2})$
groups delimited by . (\.) :
([0-9]{1,6}) - 1-6 digits
(.{1,2}) - 1-2 any single character
(0[1-2]) - 01 or 02
(.{1,2}) - 1-2 any single character
you can write and easy test regex on your input data, just google "regex online"

Regex Substring or Left Equivalent

Greetings beloved comrades.
I cannot figure out how to accomplish the following via a regex.
I need to take this format number 201101234 and transform it to 11-0123401, where digits 3 and 4 become the digits to the left of the dash, and the remaining five digits are inserted to the right of the dash, followed by a hardcoded 01.
I've tried http://gskinner.com/RegExr, but the syntax just defeats me.
This answer, Equivalent of Substring as a RegularExpression, sounds promising, but I can't get it to parse correctly.
I can create a SQL function to accomplish this, but I'd rather not hammer my server in order to reformat some strings.
Thanks in advance.

You can try this:
var input = "201101234";
var output = Regex.Replace(input, #"^\d{2}(\d{2})(\d{5})$", "${1}-${2}01");
Console.WriteLine(output); // 11-0123401
This will match:
two digits, followed by
two digits captured as group 1, followed by
five digits captured as group 2
And return a string which replaces that matched text with
group 1, followed by
a literal hyphen, followed by
group 2, followed by
a literal 01.
The start and end anchors ( ^ / $ ) ensure that if the input string does not exactly match this pattern, it will simply return the original string.

If you can use custom C# scripts, you may want to use Substring instead:
string newStr = string.Format("{0}-{1}01", old.Substring(2,2), old.Substring(4));

I don't think you really need a regex here. Substring would be better. But still if you want regex only, you can use this:
string newString = Regex.Replace(input, #"^\d{2}(\d{2})(\d+)$", "$1-${2}01");
Explanation:
^\d{2} // Match first 2 digits. Will be ignored
(\d{2}) // Match next 2 digits. Capture it in group 1
(\d+)$ // Match rest of the digits. Capture it in group 2
Now, the required digits, are in group 1 and 2, which you use in the replacement string.

Do you even SQL? Pull some levers and stuff.

Regex pattern allowing alphabets, numbers, decimals, spaces and underscore

I am not good with regular expression patterns.
I have to put a validation on an string, to allow
only alphabets, numbers, decimals, spaces, comma and underscore
for allowing the alphabets and spaces I have /^[a-zA-Z][a-zA-Z\\s]+$/
Please help me in creating all the above conditions in one pattern.
Thanks

this regex should work for your requirements
'[a-zA-Z0-9_. ,]*'
In the regex, I specified the range a to z, A to Z (uppercase), 0 to 9 and the single character _, decimal point ".", space and a comma.
If you want to make sure you want at least one character after the first letter, you can replace the * with a +, or {2,} with at least 2 more characters, or {2,5} with between 2 and 5 characters.

You can try:
/^[\w., ]+$/
I don't know what are the requirements for the starting char, if there are any.

Rahul's answer gave me the direction to think, but for the visitors, may be this too can be helpfull
patternForClasName = /^([a-zA-Z0-9 _]+\.)*[a-zA-Z0-9 _]+$/;
// Allowing valid className which has a format abcsasa.dsd.dsd(the class or a package name can have an underscore or a numerical)
patternForName = /^([a-zA-Z0-9 _-]+)$/;
// Allowing alphanumeric + spaces + (_)underscore and a (-)dash
patternForDescription = /^([a-zA-Z0-9 _-]+[\,\.]+)*[a-zA-Z0-9 _-]*$/;
// Allowing alphanumeric,spaces, (_)underscore, (-)dash, comma, decimal
patternURLFormat = /(ftp|http|https):\/\/(\w+:{0,1}\w*#)?(\S+)(:[0-9]+)?(\/|\/([\w#!:.?+=&%#!\-\/]))?/;
// For a valid URL

regex issue c# numbers are underscores now

My Regex is removing all numeric (0-9) in my string.
I don't get why all numbers are replaced by _
EDIT: I understand that my "_" regex pattern changes the characters into underscores. But not why numbers!
Can anyone help me out? I only need to remove like all special characters.
See regex here:
string symbolPattern = "[!##$%^&*()-=+`~{}'|]";
Regex.Replace("input here 12341234" , symbolPattern, "_");
Output: "input here ________"

The problem is your pattern uses a dash in the middle, which acts as a range of the ascii characters from ) to =. Here's a breakdown:
): 41
1: 49
=: 61
As you can see, numbers start at 49, and falls between the range of 41-61, so they're matched and replaced.
You need to place the - at either the beginning or end of the character class for it to be matched literally rather than act as a range:
"[-!##$%^&*()=+`~{}'|]"

you must escape - because sequence [)-=] contains digits
string symbolPattern = "[!##$%^&*()\-=+`~{}'|]";

Move the - to the end of the list so it is seen as a literal:
"[!##$%^&*()=+`~{}'|-]"
Or, to the front:
"[-!##$%^&*()=+`~{}'|]"
As it stands, it will match all characters in the range )-=, which includes all numerals.

You need to escape your special characters in your regex. For instance, * is a wildcard match. Look at what some of those special characters mean for your match.

I've not used C#, but typically the "*" character is also a control character that would need escaping.
The following matches a whole line of any characters, although the "^" and "$" are some what redundant:
^.*$
This matches any number of "A" characters that appear in a string:
A*
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Regular Expression: single word

I want to check in a C# program, if a user input is a single word. The word my only have characters A-Z and a-z. No spaces or other characters.
I try [A-Za-z]* , but this doesn't work. What is wrong with this expression?
Regex regex = new Regex("[A-Za-z]*");
if (!regex.IsMatch(userinput);)
{
...
}
Can you recomend website with a comprensiv list of regex examples?!

It probably works, but you aren't anchoring the regular expression. You need to use ^ and $ to anchor the expression to the beginning and end of the string, respectively:
Regex regex = new Regex("^[A-Za-z]+$");
I've also changed * to + because * will match 0 or more times while + will match 1 or more times.

You should add anchors for start and end of string: ^[A-Za-z]+$

Regarding the question of regex examples have a look at http://regexlib.com/.
For the regex, have a look at the special characters ^ and $, which represent starting and ending of string. This site can come in handy when constructing regexes in the future.

The asterisk character in regex specifies "zero or more of the preceding character class".
This explains why your expression is failing, because it will succeed if the string contains zero or more letters.
What you probably intended was to have one or more letters, in which case you should use the plus sign instead of the asterisk.
Having made that change, now it will fail if you enter a string that doesn't contain any letters, as you intended.
However, this still won't work for you entirely, because it will allow other characters in the string. If you want to restrict it to only letters, and nothing else, then you need to provide the start and end anchors (^ and $) in your regex to make the expression check that the 'one or more letters' is attached to the start and end of the string.
^[a-zA-Z]+$
This should work as intended.
Hope that helps.
For more information on regex, I recommend http://www.regular-expressions.info/reference.html as a good reference site.

I don't know what the C#'s regex syntax is, but try [A-Za-z]+.

Try ^[A-Za-z]+$ If you don't include the ^$ it will match on any part of the string that has a alpha characters in it.

I know the question is only about strictly alphabetic input, but here's an interesting way of solving this which does not break on accented letters and other such special characters.
The regex "^\b.+?\b" will match the first word on the start of a string, but only if the string actually starts with a valid word character. Using that, you can simply check if A) the string matches, and B) the length of the matched string equals your full string's length:
public Boolean IsSingleWord(String userInput)
{
Regex firstWordRegex = new Regex("^\\b.+?\\b");
Match firstWordMatch = firstWordRegex.Match(userInput);
return firstWordMatch.Success && firstWordMatch.Length == userInput.Length;
}

The other persons have wrote how to resolve the problem you know. Now I'll speak about the problem you perhaps don't know: diacritics :-) Your solution doesn't support àèéìòù and many other letters. A correct solution would be:
^(\p{L}\p{M}*)+$
where \p{L} is any letter plus \p{M}* that is 0 or more diacritic marks (in unicode diacritics can be "separated" from base letters, so you can have something like a + ` = à or you can have precomposed characters like the standard à)

if you just need the characters a-zA-Z you could simply iterate over the characters and compare the single characters if they are inside your range
for example:
for each character c: ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z')
This could increase your performance