Regular Expressions 101

Explanation
Pro

^start of line

Positive Lookahead(?=[\w\[\]]{6,20}$)

Character Class[\w\[\]]{6,20}

{6,20}matches between 6 and 20 characters from the set below:

\wany word character

\[the literal [ (91₁₀ / 133₈ / 5B₁₆)

\]the literal ] (93₁₀ / 135₈ / 5D₁₆)

$end of line

Character Class[A-Z]+

+matches at least one character from the set below:

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

\[the literal [ (91₁₀ / 133₈ / 5B₁₆)

\d+a digit, repeated at least once

\]the literal ] (93₁₀ / 135₈ / 5D₁₆)

Character Class[A-Z]+

+matches at least one character from the set below:

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

$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.

25 tokens

^(?=[\w\[\]]{6,20}$)[A-Z]+\[\d+\][A-Z]+$

New

ABC[15]WHATEVER
ABC[15]WHATEVERWHATER
C[15]C
ABC[15]

ABC[15]WHATEVER
ABC[15]WHATEVERWHATER
C[15]C
ABC[15]