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Can anyone improve this 'list of IP addresses' regex? [duplicate]

What is the regular expression to validate a comma delimited list like this one:
12365, 45236, 458, 1, 99996332, ......

I suggest you to do in the following way:
(\d+)(,\s*\d+)*
which would work for a list containing 1 or more elements.

This regex extracts an element from a comma separated list, regardless of contents:
(.+?)(?:,|$)
If you just replace the comma with something else, it should work for any delimiter.

It depends a bit on your exact requirements. I'm assuming: all numbers, any length, numbers cannot have leading zeros nor contain commas or decimal points. individual numbers always separated by a comma then a space, and the last number does NOT have a comma and space after it. Any of these being wrong would simplify the solution.
([1-9][0-9]*,[ ])*[1-9][0-9]*
Here's how I built that mentally:
[0-9] any digit.
[1-9][0-9]* leading non-zero digit followed by any number of digits
[1-9][0-9]*, as above, followed by a comma
[1-9][0-9]*[ ] as above, followed by a space
([1-9][0-9]*[ ])* as above, repeated 0 or more times
([1-9][0-9]*[ ])*[1-9][0-9]* as above, with a final number that doesn't have a comma.

Match duplicate comma-delimited items:
(?<=,|^)([^,]*)(,\1)+(?=,|$)
Reference.
This regex can be used to split the values of a comma delimitted list. List elements may be quoted, unquoted or empty. Commas inside a pair of quotation marks are not matched.
,(?!(?<=(?:^|,)\s*"(?:[^"]|""|\\")*,)(?:[^"]|""|\\")*"\s*(?:,|$))
Reference.

/^\d+(?:, ?\d+)*$/

i used this for a list of items that had to be alphanumeric without underscores at the front of each item.
^(([0-9a-zA-Z][0-9a-zA-Z_]*)([,][0-9a-zA-Z][0-9a-zA-Z_]*)*)$

You might want to specify language just to be safe, but
(\d+, ?)+(\d+)?
ought to work

I had a slightly different requirement, to parse an encoded dictionary/hashtable with escaped commas, like this:
"1=This is something, 2=This is something,,with an escaped comma, 3=This is something else"
I think this is an elegant solution, with a trick that avoids a lot of regex complexity:
if (string.IsNullOrEmpty(encodedValues))
{
return null;
}
else
{
var retVal = new Dictionary<int, string>();
var reFields = new Regex(#"([0-9]+)\=(([A-Za-z0-9\s]|(,,))+),");
foreach (Match match in reFields.Matches(encodedValues + ","))
{
var id = match.Groups[1].Value;
var value = match.Groups[2].Value;
retVal[int.Parse(id)] = value.Replace(",,", ",");
}
return retVal;
}
I think it can be adapted to the original question with an expression like #"([0-9]+),\s?" and parse on Groups[0].
I hope it's helpful to somebody and thanks for the tips on getting it close to there, especially Asaph!

In JavaScript, use split to help out, and catch any negative digits as well:
'-1,2,-3'.match(/(-?\d+)(,\s*-?\d+)*/)[0].split(',');
// ["-1", "2", "-3"]
// may need trimming if digits are space-separated

The following will match any comma delimited word/digit/space combination
(((.)*,)*)(.)*

Why don't you work with groups:
^(\d+(, )?)+$

If you had a more complicated regex, i.e: for valid urls rather than just numbers. You could do the following where you loop through each element and test each of them individually against your regex:
const validRelativeUrlRegex = /^(^$|(?!.*(\W\W))\/[a-zA-Z0-9\/-]+[^\W_]$)/;
const relativeUrls = "/url1,/url-2,url3";
const startsWithComma = relativeUrls.startsWith(",");
const endsWithComma = relativeUrls.endsWith(",");
const areAllURLsValid = relativeUrls
.split(",")
.every(url => validRelativeUrlRegex.test(url));
const isValid = areAllURLsValid && !endsWithComma && !startsWithComma

Regular expression match between string and last digit

I'm trying to come up with a regular expression matches the text in bold in all the examples.
Between the string "JZ" and any character before "-"
JZ123456789-301A
JZ134255872-22013
Between the string "JZ" and the last character
JZ123456789D
I have tried the following but it only works for the first example
(?<=JZ).*(?=-)

You can use (?<=JZ)[0-9]+, presuming the desired text will always be numeric.
Try it out here

You may use
JZ([^-]*)(?:-|.$)
and grab Group 1 value. See the regex demo.
Details
JZ - a literal substring
([^-]*) - Capturing group 1: zero or more chars other than -
(?:-|.$) - a non-capturing group matching either - or any char at the end of the string
C# code:
var m = Regex.Match(s, #"JZ([^-]*)(?:-|.$)");
if (m.Success)
{
Console.WriteLine(m.Groups[1].Value);
}
If, for some reason, you need to obtain the required value as a whole match, use lookarounds:
(?<=JZ)[^-]*(?=-|.$)
See this regex variation demo. Use m.Value in the code above to grab the value.

A one-line answer without regex:
string s,r;
// if your string always starts with JZ
s = "JZ123456789-301A";
r = string.Concat(s.Substring(2).TakeWhile(char.IsDigit));
Console.WriteLine(r); // output : 123456789
// if your string starts with anything
s = "A12JZ123456789-301A";
r = string.Concat(s.Substring(s.IndexOf("JZ")).TakeWhile(char.IsDigit));
Console.WriteLine(r); // output : 123456789
Basically, we remove everything before and including the delimiter "JZ", then we take each char while they are digit. The Concat is use to transform the IEnumerable<char> to a string. I think it is easier to read.
Try it online

get an special Substring in c#

I need to extract a substring from an existing string. This String starts with uninteresting characters (include "," "space" and numbers) and ends with ", 123," or ", 57," or something like this where the numbers can change. I only need the Numbers.
Thanks

public static void Main(string[] args)
{
string input = "This is 2 much junk, 123,";
var match = Regex.Match(input, #"(\d*),$"); // Ends with at least one digit
// followed by comma,
// grab the digits.
if(match.Success)
Console.WriteLine(match.Groups[1]); // Prints '123'
}

Regex to match numbers: Regex regex = new Regex(#"\d+");
Source (slightly modified): Regex for numbers only

I think this is what you're looking for:
Remove all non numeric characters from a string using Regex
using System.Text.RegularExpressions;
...
string newString = Regex.Replace(oldString, "[^.0-9]", "");
(If you don't want to allow the decimal delimiter in the final result, remove the . from the regular expression above).

Try something like this :
String numbers = new String(yourString.TakeWhile(x => char.IsNumber(x)).ToArray());

You can use \d+ to match all digits within a given string
So your code would be
var lst=Regex.Matches(inp,reg)
.Cast<Match>()
.Select(x=x.Value);
lst now contain all the numbers
But if your input would be same as provided in your question you don't need regex
input.Substring(input.LastIndexOf(", "),input.LastIndexOf(","));

Using Regex to determine if string contains a repeated sequence of a particular substring with comma separators and nothing else

I want to find if a string contains a repeated sequence of a known substring (with comma separators) and nothing else and return true if this is the case; otherwise false. For example: the substring is "0,8"
String A: "0,8,0,8,0,8,0,8" returns true
String B: "0,8,0,8,1,0,8,0" returns false because of '1'
I tried using the C# string functions Contains but it does not suit my requirements. I am totally new to regular expression but I feel it should be powerful enough to do this. What RegEx should I use to do this?

The pattern for a string containing nothing but a repeated number of a given substring (possibly zero of them, resulting in an empty string) is \A(?:substring goes here)*\z. The \A matches the beginning of the string, the \z the end of the string, and the (?:...)* matches 0 or more copies of anything matching the thing between the colon and the close parenthesis.
But your string doesn't actually match \A(?:0,8)*\z, because of the extra commas; an example that would match is "0,80,80,80,8". You need to account for the commas explicitly with something like \A0,8(?:,0,8)*\z.
You can build such a thing in C# thus:
string OkSubstring = "0,8";
string aOk = "0,8,0,8,0,8,0,8";
string bOK = "0,8,0,8,1,0,8,0";
Regex OkRegex = new Regex( #"\A" + OkSubstring + "(?:," + OkSubstring + #")*\z" );
OkRegex.isMatch(aOK); // True
OkRegex.isMatch(bOK); // False
That hard-codes the comma-delimiter; you could make it more general. Or maybe you just need the literal regex. Either way, that's the pattern you need.
EDIT Changed the anchors per Mike Samuel's suggestion.

Removing numbers from text using C#

I have a text file for processing, which has some numbers. I want JUST text in it, and nothing else. I managed to remove the punctuation marks, but how do I remove the numbers? I want this using C# code.
Also, I want to remove words with length greater than 10. How do I do that using Reg Expressions?

You can do this with a regex:
string withNumbers = // string with numbers
string withoutNumbers = Regex.Replace(withNumbers, "[0-9]", "");
Use this regex to remove words with more than 10 characters:
[\w]{10, 100}
100 defines the max length to match. I don't know if there is a quantifier for min length...

Only letters and nothing else (because I see you also want to remove the punctuation marks)
Regex.IsMatch(input, #"^[a-zA-Z]+$");

You can also use string.Join:
string s = "asdasdad34534t3sdf43534";
s = string.Join(null, System.Text.RegularExpressions.Regex.Split(s, "[\\d]"));

The Regex.Replace method should do the trick.
// regex to match any digit
var regex = new Regex("\d");
// replace all matches in input with empty string
var output = regex.Replace(input, String.Empty);