Regular Expressions 101

Pro

1st Alternative^\d{0,4}$

^start of line

\d{0,4}a digit, repeated between 0 and 4 times

$end of line

2nd Alternative^\d{4}-0?$

^start of line

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

-the literal - (45₁₀ / 55₈ / 2D₁₆)

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

$end of line

3rd Alternative^\d{4}-(?:0?[1-9]|1[012])(?:-(?:0?[1-9]?|[12]\d|3[01])?)?$

^start of line

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

-the literal - (45₁₀ / 55₈ / 2D₁₆)

Non-Capturing Group(?:0?[1-9]|1[012])

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[012]

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

Character Class[012]

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

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

?repeats the group contents below at most once:

-the literal - (45₁₀ / 55₈ / 2D₁₆)

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

?repeats the group contents below at most once:

1st Alternative0?[1-9]?

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

Character Class[1-9]?

?matches at most one character from the set below:

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

2nd Alternative[12]\d

Character Class[12]

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

\da digit

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

Detailed match information will be displayed here automatically.

26 tokens

Regular Expression

^\d{0,4}$|^\d{4}-0?$|^\d{4}-(?:0?[1-9]|1[012])(?:-(?:0?[1-9]?|[12]\d|3[01])?)?$

New

Extraction