Regular Expressions 101

1st Alternative(?<=Feb )([1-2][0-9])

Positive Lookbehind(?<=Feb )

Feb the literal text Feb (case sensitive)

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

Character Class[1-2]

1-2one character from 1 (49₁₀) to 2 (50₁₀)

Character Class[0-9]

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

2nd Alternative(?<=Mar )([1-2][0-9]|3[0-1])

Positive Lookbehind(?<=Mar )

Mar the literal text Mar (case sensitive)

Group 2([1-2][0-9]|3[0-1])

1st Alternative[1-2][0-9]

Character Class[1-2]

1-2one character from 1 (49₁₀) to 2 (50₁₀)

Character Class[0-9]

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

2nd Alternative3[0-1]

3the literal 3 (51₁₀ / 63₈ / 33₁₆)

Character Class[0-1]

0-1one character from 0 (48₁₀) to 1 (49₁₀)

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

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Search reference

Regular Expression

(?<=Feb )([1-2][0-9])|(?<=Mar )([1-2][0-9]|3[0-1])

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