regular expression to match a pattern

I need a regular expression for c# which can match following pattern

abc1abcd

1abcdefg

abcdefg1

basically my expression should have at least one number and min size is 8 char including number. If possible explain the regex开发者_开发百科 also.

I'd probably check with two statements. Just check the length eg

string.Length > 7

and then make sure it this regex can find a match...

[0-9]

You can use a look-ahead assertion to verify the length, and then search forward for a digit, thus:

(?=.{8}).*[0-9]

We look-ahead for 8 characters, and if that is successful, then we actually attempt to match "anything, followed by a digit".

But really, don't do this. Just check the length explicitly. It's much clearer.

Your regular expression pattern should just be: \d+ (match 1 or more numbers). For your example, it's probably best to not determine minimum length using regex since all you care about is that it has at least 1 number and is at least than 8 characters

Regex regEx = new Regex(@"\d+");
isValid = regEx.Match(myString).Success && myString.Length >= 8;

The pattern \d is just the same as [0-9] and the + symbol means at least one of. The @ symbol in front of the string is so that it what try to escape \d.

As mentioned by El Ronnoco in the comments, just \d would match your requirement. Knowing about \d+ is useful for more complicated patterns where you want a few numbers in between some strings,etc.

Also: I've just read something that I didn't know. \d matches any character in the Unicode number, decimal digit category which is a lot more than just [0-9]. Something to be aware of if you just want any number. Otherwise El Ronnoco's answer of [0-9] for your pattern is sufficient.