Regular Expressions 101

\ban ASCII word boundary

Group 1((?(?<=\d{4})-?|)(\d)(?!\2{3}|\2{2}-\2|\2-\2{2}|-\2{3})){16}

{16}repeats the group contents below exactly 16 times:

Condition(?(?<=\d{4})-?|)

Uses the first branch if the lookaround matches

Positive Lookbehind(?<=\d{4})

\d{4}a digit, repeated exactly 4 times

If the condition is true, match this branch:-?

-?optionally matches the literal - (45₁₀ / 55₈ / 2D₁₆)

Otherwise, match this branch: — matches an empty string

Group 2(\d)

\da digit

Negative Lookahead(?!\2{3}|\2{2}-\2|\2-\2{2}|-\2{3})

1st Alternative\2{3}

\2{3}the text saved by group 2, repeated exactly 3 times

2nd Alternative\2{2}-\2

\2{2}the text saved by group 2, repeated exactly 2 times

-the literal - (45₁₀ / 55₈ / 2D₁₆)

\2the text saved by group 2

3rd Alternative\2-\2{2}

\2the text saved by group 2

-the literal - (45₁₀ / 55₈ / 2D₁₆)

\2{2}the text saved by group 2, repeated exactly 2 times

4th Alternative-\2{3}

-the literal - (45₁₀ / 55₈ / 2D₁₆)

\2{3}the text saved by group 2, repeated exactly 3 times

\ban ASCII word boundary

Global pattern flags

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

Detailed match information will be displayed here automatically.

25 tokens

Regular Expression

\b((?(?<=\d{4})-?|)(\d)(?!\2{3}|\2{2}-\2|\2-\2{2}|-\2{3})){16}\b

New

5123-4567-8912-3456
6123456789123456
4123356789123456
5133336789123456
1234567890134443
123-4567-8901-23456
1234-4567890123456

5123-4567-8912-3456
6123456789123456
4123356789123456
5133336789123456
1234567890134443
123-4567-8901-23456
1234-4567890123456