regex101: PCRE (Legacy) Match Workspace

Pro

Negative Lookbehind(?<!\d)

\da digit

Non-Capturing Group(?:(?:20\d{2})(?:(?:(?:0[13578]|1[02])31)|(?:(?:0[1,3-9]|1[0-2])(?:29|30)))|(?:(?:20(?:0[48]|[2468][048]|[13579][26]))0229)|(?:20\d{2})(?:(?:0?[1-9])|(?:1[0-2]))(?:0?[1-9]|1\d|2[0-8]))

1st Alternative(?:20\d{2})(?:(?:(?:0[13578]|1[02])31)|(?:(?:0[1,3-9]|1[0-2])(?:29|30)))

Non-Capturing Group(?:20\d{2})

20the literal text 20

\d{2}a digit, repeated exactly 2 times

Non-Capturing Group(?:(?:(?:0[13578]|1[02])31)|(?:(?:0[1,3-9]|1[0-2])(?:29|30)))

1st Alternative(?:(?:0[13578]|1[02])31)

Non-Capturing Group(?:(?:0[13578]|1[02])31)

Non-Capturing Group(?:0[13578]|1[02])

1st Alternative0[13578]

0the 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)

31the literal text 31

2nd Alternative(?:(?:0[1,3-9]|1[0-2])(?:29|30))

Non-Capturing Group(?:(?:0[1,3-9]|1[0-2])(?:29|30))

Non-Capturing Group(?:0[1,3-9]|1[0-2])

1st Alternative0[1,3-9]

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

Character Class[1,3-9]

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

,the literal , (44₁₀ / 54₈ / 2C₁₆)

3-9one character from 3 (51₁₀) 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)

Non-Capturing Group(?:29|30)

1st Alternative29

29the literal text 29

2nd Alternative30

30the literal text 30

2nd Alternative(?:(?:20(?:0[48]|[2468][048]|[13579][26]))0229)

Non-Capturing Group(?:(?:20(?:0[48]|[2468][048]|[13579][26]))0229)

Non-Capturing Group(?:20(?:0[48]|[2468][048]|[13579][26]))

20the literal text 20

Non-Capturing Group(?:0[48]|[2468][048]|[13579][26])

0229the literal text 0229

3rd Alternative(?:20\d{2})(?:(?:0?[1-9])|(?:1[0-2]))(?:0?[1-9]|1\d|2[0-8])

Negative Lookahead(?!\d)

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

25 tokens

Regular Expression

(?<!\d)(?:(?:20\d{2})(?:(?:(?:0[13578]|1[02])31)|(?:(?:0[1,3-9]|1[0-2])(?:29|30)))|(?:(?:20(?:0[48]|[2468][048]|[13579][26]))0229)|(?:20\d{2})(?:(?:0?[1-9])|(?:1[0-2]))(?:0?[1-9]|1\d|2[0-8]))(?!\d)

New

aaa_20150229_bbb
aaa_20120229_bbb
aaa_20000229_bbb
aaa_19000229_bbb
aaa_18000229_bbb
aaa_17000229_bbb
aaa_16000229_bbb

aaa_20150130_bbb
aaa_20150131_bbb
aaa_20150430_bbb
aaa_20150431_bbb

Extraction

aaa_20150229_bbb
aaa_20120229_bbb
aaa_20000229_bbb
aaa_19000229_bbb
aaa_18000229_bbb
aaa_17000229_bbb
aaa_16000229_bbb

aaa_20150130_bbb
aaa_20150131_bbb
aaa_20150430_bbb
aaa_20150431_bbb