创建正则表达式以匹配带有字母和后跟固定位数的字符串

Question

We have one of use case where we need to validate some Uid with following constraint:

Uid of lenght 5 in form annnnn where a is any letter other than A , B , D and E . And n is any number from 0 to 9 .

So I have create new method which will validate same and working for as expected.

/// <summary>
/// Validate Uid of lenght 5 in form annnnn where ‘a’ is any letter other than A, B, D and E.
/// </summary>
/// <param name="value"></param>
/// <returns></returns>
private static bool IsValidUid( string value )
{
    bool returnValue = false;

    if (string.IsNullOrEmpty(value) == false && value.Length == 5)
    {
        char firstChar = value[0];
        bool firstCharFailed = false;

        switch (firstChar)
        {
            case 'A':
            case 'B':
            case 'D':
            case 'E':
                firstCharFailed = true;
                break;
        }

        if (firstCharFailed == false)
        {
            string remainingStr = value.Substring(1, 4);

            int numb;

            if (int.TryParse(remainingStr, out numb) == true)
            {
                returnValue = true;
            }
        }
    }

    return returnValue;
}

But it could be effectively done via regular expression. Since I am bad with it, I need help to create one for me! Thanks in advance!!

Answer 1

where 'a' is any letter other than A, B, D and E.

So in this case you need to specify the set of letters that are allowed

[a-zF-ZC] => meaning all letters are in the range az and FZ should be matched, also C should be matched

And 'n' is any number from 0 to 9.

\\d matches a digit or you can use [0-9]

of lenght 5 in form annnnn

\\d{4} specifies the amount of the preceding character that is ought to be matched

One last thing has to be done. You need to specify, that a is supposed to be at the beginning of the string and that the string ends after the 5-th character:

^ denotes the start of a string
$ denotes the end of a string.

So combined it would look like this:

string pattern = @"^[a-zF-ZC]\d{4}$

or using the range for the digits:

string pattern = @"^[a-zF-ZC][0-9]{4}$

Here is an overview of the regex patterns with examples and explanations

Here is a site where you can test and try out your regex pattern . Fiddle around with it to get to know it. It helps

EDIT:

the [...] denote a set of characters that will be matched. A Range is denoted using the - sign like in az , AF or 5-9 . Any other character ca be simply put into the set:

[abcdefgxyz] will match only those specified letters!

The set and the ranges can be combined

[CF-SX-Z] will match C or all capital letters between F and S and between X and Z . I hope it get more clear now