Regular Expressions 101

^start of line

Negative Lookahead(?!.{12})

.{12}any character (except for line terminators), repeated exactly 12 times

Character Class[A-Z0-9]+

+matches at least one character from the set below:

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

0-9one character from 0 (48₁₀) to 9 (57₁₀)

Non-Capturing Group(?:[- ][A-Z0-9]+)?

?repeats the group contents below at most once:

Character Class[- ]

-the literal - (45₁₀ / 55₈ / 2D₁₆)

the literal (32₁₀ / 40₈ / 20₁₆)

Character Class[A-Z0-9]+

+matches at least one character from the set below:

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

0-9one character from 0 (48₁₀) to 9 (57₁₀)

$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

^(?!.{12})[A-Z0-9]+(?:[- ][A-Z0-9]+)?$

New

A
ABC
ABC 01234
ABC-123
-ABC
ABC-
ABC 
 
ABC123456789
ABC12345678