Regular Expressions 101

Pro

^start of line

Group 1(19|20)

1st Alternative19

19the literal text 19

2nd Alternative20

20the literal text 20

\d{2}a Unicode decimal digit, repeated exactly 2 times

Non-Capturing Group(?:-(?:0[1-9]|1[0-2])(?:-(?:0[1-9]|[12][0-9]|3[01]))?)?

?repeats the group contents below at most once:

-the literal - (45₁₀ / 55₈ / 2D₁₆)

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

1st Alternative0[1-9]

0the 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)

Non-Capturing Group(?:-(?:0[1-9]|[12][0-9]|3[01]))?

?repeats the group contents below at most once:

-the literal - (45₁₀ / 55₈ / 2D₁₆)

Non-Capturing Group(?:0[1-9]|[12][0-9]|3[01])

1st Alternative0[1-9]

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

Character Class[1-9]

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

2nd Alternative[12][0-9]

Character Class[12]

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

Character Class[0-9]

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

3rd Alternative3[01]

3the literal 3 (51₁₀ / 63₈ / 33₁₆)

Character Class[01]

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

$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

No unit tests · Add a test to get started

25 tokens

^(19|20)\d{2}(?:-(?:0[1-9]|1[0-2])(?:-(?:0[1-9]|[12][0-9]|3[01]))?)?$

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