Regular Expressions 101

Explanation

Pro

1st Alternative^(?<Monthswith31>31(?<s1>\/|\.|-)(0?[13578]|1[02]|(Jan|Mar|May|Jul|Aug|Oct|Dec))\g<s1>(?<Year>19[0-9][0-9]|200[0-7]))$

^start of line

Group Monthswith31(?<Monthswith31>31(?<s1>\/|\.|-)(0?[13578]|1[02]|(Jan|Mar|May|Jul|Aug|Oct|Dec))\g<s1>(?<Year>19[0-9][0-9]|200[0-7]))

31the literal text 31

Group s1(?<s1>\/|\.|-)

1st Alternative\/

\/the literal / (47₁₀ / 57₈ / 2F₁₆)

2nd Alternative\.

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

3rd Alternative-

-the literal - (45₁₀ / 55₈ / 2D₁₆)

Group 3(0?[13578]|1[02]|(Jan|Mar|May|Jul|Aug|Oct|Dec))

1st Alternative0?[13578]

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

Character Class[13578]

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

3the literal 3 (51₁₀ / 63₈ / 33₁₆)

5the literal 5 (53₁₀ / 65₈ / 35₁₆)

7the literal 7 (55₁₀ / 67₈ / 37₁₆)

8the literal 8 (56₁₀ / 70₈ / 38₁₆)

2nd Alternative1[02]

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

Character Class[02]

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

3rd Alternative(Jan|Mar|May|Jul|Aug|Oct|Dec)

Group 4(Jan|Mar|May|Jul|Aug|Oct|Dec)

1st AlternativeJan

Janthe literal text Jan (case sensitive)

2nd AlternativeMar

Marthe literal text Mar (case sensitive)

3rd AlternativeMay

Maythe literal text May (case sensitive)

4th AlternativeJul

Julthe literal text Jul (case sensitive)

5th AlternativeAug

Augthe literal text Aug (case sensitive)

6th AlternativeOct

Octthe literal text Oct (case sensitive)

7th AlternativeDec

Decthe literal text Dec (case sensitive)

\g<s1>calls group s1 as a subroutine

Group Year(?<Year>19[0-9][0-9]|200[0-7])

1st Alternative19[0-9][0-9]

19the literal text 19

Character Class[0-9]

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

Character Class[0-9]

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

2nd Alternative200[0-7]

200the literal text 200

Character Class[0-7]

$end of line

2nd Alternative^(?<Monthswith29or30>(29|30)(?<s2>\/|\.|-)(0?[1,3-9]|1[0-2]|(Jan|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec))\g<s2>(?<Year2>19[0-9][0-9]|200[0-7]))$

3rd Alternative^(?<Allmonthswith28>(0?[1-9]|1[0-9]|2[0-8])(?<s3>\/|\.|-)(0?[1-9]|1[0-2]|(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec))\g<s3>(?<Year3>19[0-9][0-9]|200[0-7]))$

4th Alternative^(?<FebLeapYears>29(?<s4>\/|\.|-)(0?2|Feb)\g<s4>(19([02468][048]|[13579][26])|200[04]))$

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

Unit Test Summary

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Quick Reference

25 tokens

Regular Expression

^(?<Monthswith31>31(?<s1>\/|\.|-)(0?[13578]|1[02]|(Jan|Mar|May|Jul|Aug|Oct|Dec))\g<s1>(?<Year>19[0-9][0-9]|200[0-7]))$|^(?<Monthswith29or30>(29|30)(?<s2>\/|\.|-)(0?[1,3-9]|1[0-2]|(Jan|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec))\g<s2>(?<Year2>19[0-9][0-9]|200[0-7]))$|^(?<Allmonthswith28>(0?[1-9]|1[0-9]|2[0-8])(?<s3>\/|\.|-)(0?[1-9]|1[0-2]|(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec))\g<s3>(?<Year3>19[0-9][0-9]|200[0-7]))$|^(?<FebLeapYears>29(?<s4>\/|\.|-)(0?2|Feb)\g<s4>(19([02468][048]|[13579][26])|200[04]))$

Unit Tests

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