Regular Expressions 101

^start of line

Positive Lookahead(?=.{8}$)

.{8}any character (except for line terminators), repeated exactly 8 times

$end of line

Non-Capturing Group(?:\d*[a-z]){2}

{2}repeats the group contents below exactly 2 times:

\d*a digit, repeated any number of times

Character Class[a-z]

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.

Search reference

Regular Expression

^(?=.{8}$)(?:\d*[a-z]){2}\d*$

New

a123456b
1a2b3456
aa123456
123ab456
And the bad samples:

1abcdefg2
a1234567b
abcdefgh
12345678