regex101: PCRE (Legacy) Match Workspace

Comment: Leap Years are any year that can be evenly divided by 4

Comment: (such as 2012, 2016, etc)

Comment: • except if it can be evenly divided by 100

Comment: then it isn't (such as 2100, 2200, etc)

Comment: • except if it can be evenly divided by 400,

Comment: then it is (such as 2000, 2400)

Comment: https://www.mathsisfun.com/leap-years.html

Comment: -------------------------------------------------

Comment: verify date dd/mm/yyyy; possible separators: -.,/

Comment: valid year range: 0000-9999

^start of line

Comment: start anchor

Comment: precheck xx-xx-xxxx,... add new separators here

Positive Lookahead(?=\d{2}([-.,\/])\d{2}\1\d{4}$)

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

Group 1([-.,\/])

Character Class[-.,\/]

-the literal - (45₁₀ / 55₈ / 2D₁₆)

.the literal . (46₁₀ / 56₈ / 2E₁₆)

,the literal , (44₁₀ / 54₈ / 2C₁₆)

\/the literal / (47₁₀ / 57₈ / 2F₁₆)

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

\1the text saved by group 1

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

$end of line

Non-Capturing Group(?: # day-check: non caturing group # days 01-28 0[1-9]|1\d|[2][0-8]| # february 29d check for leap year: all 4y / 00 years: only each 400 # 0400,0800,1200,1600,2000,... 29 (?!.02. # not if feb: if not ... (?! # 00 years: exclude !0 %400 years (?!(?:[02468][1-35-79]|[13579][0-13-57-9])00) # 00,04,08,12,... \d{2}(?:[02468][048]|[13579][26]) ) )| # d30 negative lookahead: february cannot have 30 days 30(?!.02)| # d31 positive lookahead: month up to 31 days 31(?=.(?:0[13578]|10|12)) )

1st Alternative # day-check: non caturing group # days 01-28 0[1-9]

Comment: day-check: non caturing group

Comment: days 01-28

0the literal text 0

Character Class[1-9]

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

2nd Alternative1\d

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

\da digit

3rd Alternative[2][0-8]

Character Class[2]

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

Character Class[0-8]

0-8one character from 0 (48₁₀) to 8 (56₁₀)

4th Alternative # february 29d check for leap year: all 4y / 00 years: only each 400 # 0400,0800,1200,1600,2000,... 29 (?!.02. # not if feb: if not ... (?! # 00 years: exclude !0 %400 years (?!(?:[02468][1-35-79]|[13579][0-13-57-9])00) # 00,04,08,12,... \d{2}(?:[02468][048]|[13579][26]) ) )

Comment: february 29d check for leap year: all 4y / 00 years: only each 400

Comment: 0400,0800,1200,1600,2000,...

29 the literal text 29

Negative Lookahead(?!.02. # not if feb: if not ... (?! # 00 years: exclude !0 %400 years (?!(?:[02468][1-35-79]|[13579][0-13-57-9])00) # 00,04,08,12,... \d{2}(?:[02468][048]|[13579][26]) ) )

.any character (except for line terminators)

02the literal text 02

.any character (except for line terminators)

Comment: not if feb: if not ...

Negative Lookahead(?! # 00 years: exclude !0 %400 years (?!(?:[02468][1-35-79]|[13579][0-13-57-9])00) # 00,04,08,12,... \d{2}(?:[02468][048]|[13579][26]) )

Comment: 00 years: exclude !0 %400 years

Negative Lookahead(?!(?:[02468][1-35-79]|[13579][0-13-57-9])00)

Non-Capturing Group(?:[02468][1-35-79]|[13579][0-13-57-9])

1st Alternative[02468][1-35-79]

Character Class[02468]

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

4the literal 4 (52₁₀ / 64₈ / 34₁₆)

6the literal 6 (54₁₀ / 66₈ / 36₁₆)

8the literal 8 (56₁₀ / 70₈ / 38₁₆)

Character Class[1-35-79]

1-3one character from 1 (49₁₀) to 3 (51₁₀)

5-7one character from 5 (53₁₀) to 7 (55₁₀)

9the literal 9 (57₁₀ / 71₈ / 39₁₆)

2nd Alternative[13579][0-13-57-9]

Character Class[13579]

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

3the literal 3 (51₁₀ / 63₈ / 33₁₆)

5the literal 5 (53₁₀ / 65₈ / 35₁₆)

7the literal 7 (55₁₀ / 67₈ / 37₁₆)

9the literal 9 (57₁₀ / 71₈ / 39₁₆)

Character Class[0-13-57-9]

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

3-5one character from 3 (51₁₀) to 5 (53₁₀)

7-9one character from 7 (55₁₀) to 9 (57₁₀)

00the literal text 00

Comment: 00,04,08,12,...

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

Non-Capturing Group(?:[02468][048]|[13579][26])

1st Alternative[02468][048]

Character Class[02468]

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

4the literal 4 (52₁₀ / 64₈ / 34₁₆)

6the literal 6 (54₁₀ / 66₈ / 36₁₆)

8the literal 8 (56₁₀ / 70₈ / 38₁₆)

Character Class[048]

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

4the literal 4 (52₁₀ / 64₈ / 34₁₆)

8the literal 8 (56₁₀ / 70₈ / 38₁₆)

2nd Alternative[13579][26]

5th Alternative # d30 negative lookahead: february cannot have 30 days 30(?!.02)

6th Alternative # d31 positive lookahead: month up to 31 days 31(?=.(?:0[13578]|10|12))

Comment: eof day-check

Comment: month 01-12

.any character (except for line terminators)

Non-Capturing Group(?:0[1-9]|1[012])

Comment: year 0000-9999

.any character (except for line terminators)

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

$end of line

Comment: end anchor

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

x modifier: extended. Ignores unescaped whitespace and comments outside character classes

Search reference

Regular Expression

# Leap Years are any year that can be evenly divided by 4 
# (such as 2012, 2016, etc)
# • except if it can be evenly divided by 100
#   then it isn't (such as 2100, 2200, etc)
#   • except if it can be evenly divided by 400,
#     then it is (such as 2000, 2400)
# https://www.mathsisfun.com/leap-years.html
# -------------------------------------------------
# verify date dd/mm/yyyy; possible separators: -.,/
# valid year range: 0000-9999

^    # start anchor

# precheck xx-xx-xxxx,... add new separators here
(?=\d{2}([-.,\/])\d{2}\1\d{4}$)

(?:  # day-check: non caturing group

  # days 01-28
  0[1-9]|1\d|[2][0-8]| 

  # february 29d check for leap year: all 4y / 00 years: only each 400
  # 0400,0800,1200,1600,2000,...
  29
  (?!.02. # not if feb: if not ...
    (?!
      # 00 years: exclude !0 %400 years
      (?!(?:[02468][1-35-79]|[13579][0-13-57-9])00)

      # 00,04,08,12,... 
      \d{2}(?:[02468][048]|[13579][26])
    )
  )|

  # d30 negative lookahead: february cannot have 30 days
  30(?!.02)|

  # d31 positive lookahead: month up to 31 days
  31(?=.(?:0[13578]|10|12))

) # eof day-check

# month 01-12
.(?:0[1-9]|1[012])

# year 0000-9999
.\d{4}

$ # end anchor

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