Regular Expressions 101

^start of line

(?i)applies the following effective flags to the remainder of the pattern: gmi

i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters

Group 1(0?[1-9]|[12][0-9]|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]

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)

?optionally matches the literal (32₁₀ / 40₈ / 20₁₆)

Group 2(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec)?

?repeats the group contents below at most once:

1st AlternativeJan

Janthe literal text Jan (case insensitive)

2nd AlternativeFeb

Febthe literal text Feb (case insensitive)

3rd AlternativeMar

Marthe literal text Mar (case insensitive)

4th AlternativeApr

Aprthe literal text Apr (case insensitive)

5th AlternativeMay

Maythe literal text May (case insensitive)

6th AlternativeJun

Junthe literal text Jun (case insensitive)

7th AlternativeJul

Julthe literal text Jul (case insensitive)

8th AlternativeAug

Augthe literal text Aug (case insensitive)

9th AlternativeSep

Septhe literal text Sep (case insensitive)

10th AlternativeOct

Octthe literal text Oct (case insensitive)

11th AlternativeNov

Novthe literal text Nov (case insensitive)

12th AlternativeDec

Decthe literal text Dec (case insensitive)

?optionally matches the literal (32₁₀ / 40₈ / 20₁₆)

Group 3(\d{4})?

?repeats the group contents below at most once:

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

$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.

Search reference

Regular Expression

^(?i)(0?[1-9]|[12][0-9]|3[01])? ?(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec)? ?(\d{4})?$

Test String
New

11
11 jun
11 Jun 2025
2025
6
Jun

Regular Expression

Test StringNew

Test String
New