Regex variable length-CodePudding

I am looking for a regex that matches:

Length is between 1 and 10.
The 8th character can be alphanumeric [0-9a-zA-Z] and the rest have to be digits [0-9]

Valid

Invalid

1a
123456789a
12345678901

I have tried: [0-9]{1,7}[0-9a-zA-Z][0-9]{0,1} but that is failing miserably

CodePudding user response：

You can match either 1-7 digits, or match 7 digits, the 8th one being [0-9a-zA-Z] and optional 2 digits.

^(?:\d{7}[\da-zA-Z]\d{0,2}|\d{1,7})$

^ Start of string
(?: Non capture group
- \d{7}[\da-zA-Z]\d{0,2} Match 7 digits and one of 0-9a-zA-Z] and 2 optional digits
- | Or
- \d{1,7} Match 1-7 digits
) Close non capture group
$ End of string

CodePudding user response：

You could try:

^(?!.{11})\d(?:\d{6}[^\W_])?\d*$

See an online demo

^ - Start-line anchor;
(?!.{11}) - Negative lookahead to prevent 11 chars;
\d - A single digit;
(?:\d{6}[^\W_])? - Optional non-capture group to match 6 more digits and any character in class [A-Za-z0-9];
\d* - 0 (Greedy) digits;
$ - End-line anchor.

CodePudding user response：

Well you could simplify The fourth birds solution by using \w

Like so:

^(?:\d{7}\w\d{0,2}|\d{1,7})$

But that’s basically the same.