Regex variable length

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

1
123
1234567890
1234567a

Invalid

1a
123456789a
12345678901

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

>Solution :

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}[0-9a-zA-Z]\d{0,2}|\d{1,7})$

• ^ Start of string
• (?: Non capture group
  • \d{7}[0-9a-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

Regex demo