Develop Reference

Regularexpression for duplicate pattern

I am trying to write a regex to handle these cases
contains only alphanumeric with minimum of 2 alpha characters(numbers are optional).
only special character allowed is hyphen.
cannot be all same letter ignoring hyphen.
cannot be all hyphens
cannot be all numeric
My regex: (?=[^A-Za-z]*[A-Za-z]){2}^[\w-]{6,40}$
Above regex works for most of the scenarios except 1) & 3).
Can anyone suggest me to fix this. I am stuck in this.
Regards,
Sajesh

Rule 1 eliminates rule 4 and 5: It can neither contain only hyphens, nor only digits.
/^(?=[a-z\d-]{6,40}$)[\d-]*([a-z]).*?(?!\1)[a-z].*$/i
(?=[a-z\d-]{6,40}$) look ahead for specified characters from 6 to 40
([a-z]).*?(?!\1)[a-z] checks for two letters and at least one different
See this demo at regex101
This pattern with i flag considers A and a as the "same" letter (caseless matching) and will require another alpbhabet. For case sensitive matching here another demo at regex101.

You can use
^(?!\d+$)(?!-+$)(?=(?:[\d-]*[A-Za-z]){2})(?![\d-]*([A-Za-z])(?:[\d-]*\1)+[\d-]*$)[A-Za-z\d-]{6,40}$
See the regex demo. If you use it in C# or PHP, consider replacing ^ with \A and $ with \z to make sure you match the entire string even in case there is a trailing newline.
Details:
^ - start of string
(?!\d+$) - fail the match if the string only consists of digits
(?!-+$) - fail the match if the string only consists of hyphens
(?=(?:[\d-]*[A-Za-z]){2}) - there must be at least two ASCII letters after any zero or more digits or hyphens
(?![\d-]*([A-Za-z])(?:[\d-]*\1)+[\d-]*$) - fail the match if the string contains two or more identical letters (the + after (?:[\d-]*\1) means there can be any one letter)
[A-Za-z\d-]{6,40} - six to forty alphanumeric or hyphen chars
$ - end of string. (\z might be preferable.)

C# Regex match only if one group of numbers is found in string

I'm trying to come up with a regex to deal with a general scenario to capture a number from a string where the number may have one or more non-numeric characters pre/post-fixed to it.
The number can contain zero or one decimal or comma.
If the string contains multiple "sets" of consecutive digits separated by non-digits I would like the regex to fail ("sets" is probably not the correct terminology).
As an example the following inputs would succeed with a match:
abc12.00xyz would match 12.00
0.1$ would be valid and match 0.1
.01 would be valid and match .01
123abc would be valid and match 123
abc123 would be valid and match 123
These inputs would fail to match:
abc12.00xyz322 would fail due to the second "set" of digits, 322 in this example
12t2 would fail due to having two separate "sets" of digits
I've tried many permutations and I'm not making much headway. This is the closest I've come to so far. It matches on the numbers correctly, excluding the non-digits from the match, but it includes all "sets" of numbers in the string.
([\d]*[.,])?[\d]+
Any suggestions would be appreciated.

You can use a capture group:
^[^0-9\r\n]*?([0-9]*\.?[0-9]+)[^0-9\r\n]*$
^ Start of string
[^0-9\r\n]* Optionally match any char except a digit or a newline, as few as possible
([0-9]*\.?[0-9]+) Capture group 1, match optional digits, optional comma and 1+ digits
[^0-9\r\n]* Optionally match any char except a digit or a newline
$ End of string
See a .NET regex demo (Click on the Table tab to see the capture group values)

How to read first set of numbers between strings using regex?

I have the following strings and need to extract the numbers as follows :
1) M123123123AD123 => 123123123
2) M1231231212MN23 => 1231231212
3) G12312312312DD => 12312312312
I am currently reading it using "\d+[0-9]". This works well if there is 1 number after the second set of characters. But if there are multiple numbers after the second character set, the above regex string picks them too. For example, 'M123123123AD123' will give 123123123123. But the last 123 should not be there.

You want to get a streak of digits in between two letters.
You can use
(?<=[a-zA-Z])\d+(?=[a-zA-Z])
See the .NET regex demo.
Or, if you want to get the digits after the leading non-digit chars, use
(?<=^\D+)\d+(?=[a-zA-Z])
See this .NET regex demo.
In C#, you can use Regex.Match:
var result = Regex.Match(text, #"(?<=^\D+)\d+(?=[a-zA-Z])")?.Value;
Regex details:
(?<=[a-zA-Z]) - right before the current location, there must be an ASCII letter (use \p{L} to match any letter)
(?<=^\D+) - right before the current location, there must be start of string + any one or more non-digit chars (use \D* if the digits can appear at the start of string)
\d+ - one or more digits
(?=[a-zA-Z]) - right after the current location, there must be an ASCII letter (use \p{L} to match any letter).

Regular Expressions C#

I know there are many questions about making regular expressions, but they all seem to be about a single problem than the general usage. I, too, have a problem like to solve. I have tried to learn by reading about regular expressions, but it gets tricky quick. Here's my question:
C#
I need to validate two textboxes that exist on the same form. The math operations I've coded can handle any floating point number. For this particular application I know of three formats the numbers will be in or there is a mistake on the users behalf. I'd like to prevent those mistakes in example if an extra number is accidentally typed or if enter is hit too early, etc.
Here are the formats: "#.####" "##.####" "###.##" where the "#" represents a mandatory digit. The formats starting with a one or two digit whole number must have 4 trailing digits or more. I've capped it at 8, or so I tried to lol.The format starting with a three digit whole number should never be allowed to have more than two digits trailing the decimal.
Here's what I have tried thus far.
Regex acceptedInputRegex = new Regex(#"^\b[0-9]{3}.[0-9]{2}|[0-9]{1,2}.[0-9]{4,8}$");
Regex acceptedInputRegex = new Regex(#"^\b\d{3}.\d{2} | \d{1,2}.\d{4,8}$");
I have tried it in thinking a match was what I wanted to achieve and as if a match to my negated expression means there is a problem. I was unsuccessful in both attempts. This is the code:
if (acceptedInputRegex.IsMatch(txtMyTextBox1.Text) || acceptedInputRegex.IsMatch(txtMyTextBox2.Text))
{
} else
{
MessageBox.Show("Numbers are not in the right format", "Invalid Input!");
return;
}
Are regular expressions what I should be using to solve this problem?
If not, please tell me what you recommend. If so, please help me correct my regex.
Thanks.

You are close, you need to escape the dots and group the alternatives so that the ^ and $ anchors could be applied to both of them:
#"^(?:\d{3}\.\d{2}|\d{1,2}\.\d{4,8})$"
See the regex demo.
Details:
^ - start of string
(?: - start of a non-capturing group matching either of the two alternatives:
\d{3}\.\d{2} - 3 digits, . and 2 digits
| - or
\d{1,2}\.\d{4,8} - 1 or 2 digits, ., 4 to 8 digits
) - end of the non-capturing group
$ - end of string.
To make \d match only ASCII digits, use RegexOptions.ECMAScript option:
var isValid = Regex.IsMatch(s, #"^(?:\d{3}\.\d{2}|\d{1,2}\.\d{4,8})$", RegexOptions.ECMAScript);

Get a number with exactly x digits from string

im looking for a regex pattern, which matches a number with a length of exactly x (say x is 2-4) and nothing else.
Examples:
"foo.bar 123 456789", "foo.bar 456789 123", " 123", "foo.bar123 " has to match only "123"
So. Only digits, no spaces, letters or other stuff.
How do I have to do it?
EDIT: I want to use the Regex.Matches() function in c# to extract this 2-4 digit number and use it in additional code.

Any pattern followed by a {m,n} allows the pattern to occur m to n times. So in your case \d{m,n} for required values of m and n. If it has to be exactly an integer, use\d{m}
If you want to match 123 in x123y and not in 1234, use \d{3}(?=\D|$)(?<=(\D|^)\d{3})
It has a look ahead to ensure the character following the 3 digits is a non-digitornothing at all and a look behind to ensure that the character before the 3 digits is a non-digit or nothing at all.

You can achieve this with basic RegEx:
\b(\d\d\d)\b or \b(\d{3})\b - for matching a number with exactly 3 digits
If you want variable digits: \b(\d{2,4})\b (explained demo here)
If you want to capture matches next to words: \D(\d{2,4})\D (explained demo here)
\b is a word boundary (does not match anything, it's a zero-match character)
\d matches only digits
\D matches any character that is NOT a digit
() everything in round brackets will capture a match