Regular Expressions 101

Explanation

Pro

^start of line

Non-Capturing Group(?:(?=[a-zA-Z\d]{8})[A-Za-z]+\d*)

Positive Lookahead(?=[a-zA-Z\d]{8})

Character Class[a-zA-Z\d]{8}

{8}matches exactly 8 characters from the set below:

a-zone character from a (97₁₀) to z (122₁₀) (case sensitive)

A-Zone character from A (65₁₀) to Z (90₁₀) (case sensitive)

\da digit

Character Class[A-Za-z]+

+matches at least one character from the set below:

A-Zone character from A (65₁₀) to Z (90₁₀) (case sensitive)

a-zone character from a (97₁₀) to z (122₁₀) (case sensitive)

\d*a digit, repeated any number of times

$end of line

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string

Detailed match information will be displayed here automatically.

26 tokens

^(?:(?=[a-zA-Z\d]{8})[A-Za-z]+\d*)$

New

abc12345
w1234567
qweqr123
jsgwiuegn1274124
qwerasdf
awdjwuadhuf

wrong examples: 
12345678
qwe12qwe
12qweqwe
qweq12