Regular Expressions 101

Explanation
Pro

^start of line

Non-Capturing Group(?:[a-zA-Z]{1,3}|(?!0*-)[0-9]{1,3})

1st Alternative[a-zA-Z]{1,3}

Character Class[a-zA-Z]{1,3}

{1,3}matches between 1 and 3 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)

2nd Alternative(?!0*-)[0-9]{1,3}

Negative Lookahead(?!0*-)

0*the literal 0 (48₁₀ / 60₈ / 30₁₆) , repeated any number of times

-the literal - (45₁₀ / 55₈ / 2D₁₆)

Character Class[0-9]{1,3}

{1,3}matches between 1 and 3 characters from the set below:

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

-the literal - (45₁₀ / 55₈ / 2D₁₆)

Character Class[0-9]{4}

{4}matches exactly 4 characters from the set below:

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

Negative Lookbehind(?<!0{4})

0{4}the literal 0 (48₁₀ / 60₈ / 30₁₆) , repeated exactly 4 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.

25 tokens

^(?:[a-zA-Z]{1,3}|(?!0*-)[0-9]{1,3})-[0-9]{4}(?<!0{4})$

New

1-0001
10-0010
111-0000
000-1112
A-3049
KJ-6825
AAC-3422

1-0001
10-0010
111-0000
000-1112
A-3049
KJ-6825
AAC-3422