Regular Expressions 101

Group 1([\d]{4})

Character Class[\d]{4}

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

\da digit

Character Class[- ]

-the literal - (45₁₀ / 55₈ / 2D₁₆)

the literal (32₁₀ / 40₈ / 20₁₆)

Group 2(0?[1-9]|1[0-2])

1st Alternative0?[1-9]

0?optionally matches the literal 0 (48₁₀ / 60₈ / 30₁₆)

Character Class[1-9]

1-9one character from 1 (49₁₀) to 9 (57₁₀)

2nd Alternative1[0-2]

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

Character Class[0-2]

0-2one character from 0 (48₁₀) to 2 (50₁₀)

Character Class[- ]

-the literal - (45₁₀ / 55₈ / 2D₁₆)

the literal (32₁₀ / 40₈ / 20₁₆)

Group 3(\d{1,4})

\d{1,4}a digit, repeated between 1 and 4 times

\ban ASCII word boundary

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

([\d]{4})[- ](0?[1-9]|1[0-2])[- ](\d{1,4})\b

New

Payment of invoice nr.2021-02-9999
Invoice 2021 3 27 has been paid
My invoice 21-3-27 Testing, should not work.
My other invoice 2021-13-27 and 2021-0-27, should not work.
My invoice 2021-1-27  and 2021-01-1234 , should both work
Invoice 2021 3 19999 has been paid