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Use OR in Regex Expression

I have a regex to match the following:
somedomain.com/services/something
Basically I need to ensure that /services is present.
The regex I am using and which is working is:
\/services*
But I need to match /services OR /servicos. I tried the following:
(\/services|\/servicos)*
But this shows 24 matches?! https://regex101.com/r/jvB1lr/1
How to create this regex?

The (\/services|\/servicos)* matches 0+ occurrences of /services or /servicos, and that means it can match an empty string anywhere inside the input string.
You can group the alternatives like /(services|servicos) and remove the * quantifier, but for this case, it is much better to use a character class [oe] as the strings only differ in 1 char.
You want to use the following pattern:
/servic[eo]s
See the regex demo
To make sure you match a whole subpart, you may append (?:/|$) at the pattern end, /servic[eo]s(?:/|$).
In C#, you may use Regex.IsMatch with the pattern to see if there is a match in a string:
var isFound = Regex.IsMatch(s, #"/servic[eo]s(?:/|$)");
Note that you do not need to escape / in a .NET regex as it is not a special regex metacharacter.
Pattern details
/ - a /
servic[eo]s - services or servicos
(?:/|$) - / or end of string.

Well the * quantifier means zero or more, so that is the problem. Remove that and it should work fine:
(\/services|\/servicos)
Keep in mind that in your example, you have a typo in the URL so it will correctly not match anything as it stands.
Here is an example with the typo in the URL fixed, so it shows 1 match as expected.

First off you specify C# (really .Net is the library which holds regex not the language) in this post but regex101 in your example is set to PHP. That is providing you with invalid information such as needed to escape a forward slash / with \/ which is unnecessary in .Net regular expressions. The regex language is the same but there are different tools which behave differently and php is not like .Net regex.
Secondly the star * on the ( ) is saying that there may be nothing in the parenthesis and your match is getting null nothing matches on every word.
Thirdly one does not need to split the whole word. I would just extract the commonality in the words into a set [ ]. That will allow the "or-ness" you need to match on either services or servicos. Such as
(/servic[oe]s)
Will inform you if services are found or not. Nothing else is needed.

How can i make my regular expression work?

I am new to both .NET (C#) and regular expressions.
I need a regular expression to match against a url:
If url string contains "/id/Whatever_COMES_HERE_EVERY_CHAR_ACCEPTED/" : return true
If url string contains only "/id/" : return false
I have tried the following but it only returns true if url is http:// localhost/id/
This is my script:
string thisUrl = HttpContext.Current.Request.Url.AbsolutePath;
Match match = Regex.Match(thisUrl, #"/id/*$");
What am i doing wrong?

You have this:
/id/*$
What this is doing is matching the literal string /id/ and then you have the quantifier * which means 0 or more times. Then you have $ which means end of the string.
You are looking for repetition of the literal / which is not what you want. (So this: http:// localhost/id/////////////////// should have matched too with your original regex)
What you need is something like this:
/id/.+$
This will match the literal /id/ followed by the . which in regex means any character which is quantified with the + which means 1 or more.
You could tighten it up and use \S instead of . which means non-whitespace characters (since a URL shouldn't have whitespace)
Also note: there are a variety of online regex tools which are really useful when trying to figure out and test a regex. A couple of examples:
http://rubular.com/
http://regex101.com/
http://www.regxlib.com/
And even extension for visual studio you can use:
https://visualstudiogallery.msdn.microsoft.com/bf883ae3-188b-43bc-bd29-6235c4195d1f

When you use the start it signals that 0 or more of the preceding char shall be present. You will want to use
"/id/.+" to signal that at least one more char must come after the /

If you're just looking for true/false solution, you should use IsMatch() function. The other issue is that * (zero or more) and + (one or more) are quantifiers and must be preceeded by a character class or group. Dot (.) is a character class that represents ANY character. So the correct solution for your problem would be:
Regex.IsMatch(thisUrl, #"/id/.+$");
Considering that the input is a URL, this regex can be improved upon by restricting character classes to valid URL characters only, but for your purpose the above should be sufficient.

Excluding certain patterns in a regex

I'm working on a Regex in C# to exclude certain patterns within a string.
These are the types patterns I want to accept are: "%00" (Hex 00-FF) and any other character without a starting '%'. The patterns I would like to exclude are: "%0" (Values with a starting % and one character after) and/or characters "&<>'/".
So far I have this
Regex correctStringRegex = new Regex(#"(%[0-9a-fA-F]{2})|[^%&<>'/]|(^(%.))",
RegexOptions.IgnoreCase);
Below are examples of what I'm trying to pass and reject.
Passing String %02This is%0A%0Da string%03
Reject String %0%0Z%A&<%0a%
If a string doesn't pass all the requirements I would like to reject the whole string completely.
Any Help would be greatly appreciated!

I suggest this:
^(?:%[0-9a-f]{2}|[^%&<>'/])*$
Explanation:
^ # Start of string
(?: # Match either
%[0-9a-f]{2} # %xx
| # or
[^%&<>'/] # any character except the forbidden ones
)* # any number of times
$ # until end of string.
This ensures that % is only matched when followed by two hexadecimals. Since you're already compiling the regex with the IgnoreCase flag set, you don't need a-fA-F, either.

Hmm, given the comments so far, I think you need a different problem definition. You want to pass or fail a string, using regex, based on whether or not the string contains any invalid patterns. Im assuming a string will fail if there is ANY invalid pattern, rather than the reverse of a string passing if there is any valid pattern.
As such, I would use this regex: %(?![0-9a-f]{2})|[&<>'/]
You would then run this in such a way that a string is invalid if you GET a match, a valid string will not have any matches in this set.
A quick explanation of a rather odd regex. The format (?!) tells the regex "Match the previous symbol if the symbols in this set DONT follow it" ie: Match if suffix not present. So, what im telling it to look for is any instance of % that is not followed by 2 hex characters, or any other invalid character. The assumption is that anything that DOESN'T match this regex is a valid character entry.

how to create regular expression based on some condition

i want to create a regular expression to find and replace uppercase character based on some condition.
find the starting uppercase for a group of uppercase character in a string and replace it lowercase and * before the starting uppercase.
If there is any lowercase following the uppercase,replace the uppercase with lowercase and * before the starting uppercase.
input string : stackOVERFlow
expected output : stack*over*flow
i tried but could not get it working perfectly.
Any idea on how to create a regular expression ?
Thanks

Well the expected inputs and outputs are slightly illogical: you're lower-casing the "f" in "flow" but not including it in the asterisk.
Anyway, the regex you want is pretty simple: #"[A-Z]+?". This matches a string of one or more uppercase alpha characters, nongreedily (don't think it makes a difference either way as the matched character class is relatively narrow).
Now, to do the find/replace, you would do something like the following:
Regex.Replace(inputString, #"([A-Z]+?)", "*$1*").ToLower();
This simply finds all occurrences of one or more uppercase alpha characters, and wherever it finds a match it replaces it with itself surrounded by asterisks. This does the surrounding but not the lowercasing; .NET Regex doesn't provide for that kind of string modification. However, since the end result of the operation should be a string with all lowercase chars, just do exactly that with a ToLower() and you'll get the expected result.

KeithS's solution can be simplified a bit
Regex.Replace("stackOVERFlow","[A-Z]+","*$0*").ToLower()
However, this will yield stack*overf*low including the f between the stars. If you want to exclude the last upper case letter, use the following expression
Regex.Replace("stackOVERFlow","[A-Z]+(?=[A-Z])","*$0*").ToLower()
It will yield stack*over*flow
This uses the pattern find(?=suffix), which finds a position before a suffix.

why do these regex tests let certain characters pass?

I am checking a string with the following regexes:
[a-zA-Z0-9]+
[A-Za-z]+
For some reason, the characters:
.
-
_
are allowed to pass, why is that?

If you want to check that the complete string consists of only the wanted characters you need to anchor your regex like follows:
^[a-zA-Z0-9]+$
Otherwise every string will pass that contains a string of the allowed characters somewhere. The anchors essentially tell the regular expression engine to start looking for those characters at the start of the string and stop looking at the end of the string.
To clarify: If you just use [a-zA-Z0-9]+ as your regex, then the regex engine would rightfully reject the string -__-- as the regex doesn't match against that. There is no single character from the character class you defined.
However, with the string a-b it's different. The regular expression engine will match the first a here since that matches the expression you entered (at least one of the given characters) and won't care about the - or the b. It has done its job and successfully matched a substring according to your regular expression.
Similarly with _-abcdef- – the regex will match the substring abcdef just fine, because you didn't tell it to match only at the start or end of the string; and ignore the other characters.
So when using ^[a-zA-Z0-9]+$ as your regex you are telling the regex engine definitely that you are looking for one or more letters or digits, starting at the very beginning of the string right until the end of the string. There is no room for other characters to squeeze in or hide so this will do what you apparently want. But without the anchors, the match can be anywhere in your search string. For validation purposes you always want to use those anchors.

In regular expressions the + tells the engine to match one or more characters.
So this expression [A-Za-z]+ passes if the string contains a sequence of 1 or more alphabetic characters. The only strings that wouldn't pass are strings that contain no alphabetic characters at all.
The ^ symbol anchors the character class to the beginning of the string and the $ symbol anchors to the end of the string.
So ^[A-Za-z0-9]+ means 'match a string that begins with a sequence of one or more alphanumeric characters'. But would allow strings that include non-alphanumerics so long as those characters were not at the beginning of the string.
While ^[A-Za-z0-9]+$ means 'match a string that begins and ends with a sequence of one or more alphanumeric characters'. This is the only way to completely exclude non-alphanumerics from a string.