Regular Expressions 101

Explanation

Pro

\ban ASCII word boundary

\d{7}a digit, repeated exactly 7 times

Positive Lookahead(?=\s+(?:0[1-9]|[12]\d|3[01])\.(?:0[1-9]|1[0-2])\.[12]\d{3})

\s+any whitespace character, repeated at least once

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

1st Alternative0[1-9]

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

Character Class[1-9]

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)

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Non-Capturing Group(?:0[1-9]|1[0-2])

1st Alternative0[1-9]

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

Character Class[1-9]

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

2nd Alternative1[0-2]

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

Character Class[0-2]

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

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Character Class[12]

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

\d{3}a digit, repeated exactly 3 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

No unit tests

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25 tokens

\b\d{7}(?=\s+(?:0[1-9]|[12]\d|3[01])\.(?:0[1-9]|1[0-2])\.[12]\d{3})

There are no unit tests.