Regular Expressions 101

^start of line

Group 1((?=3[0-1]|[0-2]\d)\d\d)

Positive Lookahead(?=3[0-1]|[0-2]\d)

1st Alternative3[0-1]

3the literal 3 (51₁₀ / 63₈ / 33₁₆)

Character Class[0-1]

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

2nd Alternative[0-2]\d

Character Class[0-2]

0-2one character from 0 (48₁₀) to 2 (50₁₀)

\da digit

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Group 2((?=1[0-2]|0[1-9])\d\d)

Positive Lookahead(?=1[0-2]|0[1-9])

1st Alternative1[0-2]

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

Character Class[0-2]

0-2one character from 0 (48₁₀) to 2 (50₁₀)

2nd Alternative0[1-9]

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

Character Class[1-9]

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

\da digit

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

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

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

^((?=3[0-1]|[0-2]\d)\d\d)\.((?=1[0-2]|0[1-9])\d\d)\.\d{4}

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