Regular Expressions 101

(?x)applies the following effective flags to the remainder of the pattern: gmx

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

Group 1(19|20)

1st Alternative19

19the literal text 19

2nd Alternative20

20the literal text 20

\da digit

Comment: year group 1

Character Class[- \.]

-the literal - (45₁₀ / 55₈ / 2D₁₆)

the literal (32₁₀ / 40₈ / 20₁₆)

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Comment: separator

Group 2(0[1-9]|1[012])

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[012]

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

Character Class[012]

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

Comment: month group 2

Character Class[- \.]

-the literal - (45₁₀ / 55₈ / 2D₁₆)

the literal (32₁₀ / 40₈ / 20₁₆)

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Comment: separator

Group 3(0[1-9]|[12][0-9]|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][0-9]

Character Class[12]

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

Character Class[0-9]

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

3rd Alternative3[01]

3the literal 3 (51₁₀ / 63₈ / 33₁₆)

Character Class[01]

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

Comment: day group 3

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

Detailed match information will be displayed here automatically.

25 tokens

Regular Expression

(?x)
(19|20)\d\d                (?# year group 1)
[- \.]                     (?# separator)
(0[1-9]|1[012])            (?# month group 2)
[- \.]                     (?# separator)
(0[1-9]|[12][0-9]|3[01])   (?# day group 3)

New

2020-10-12

Substitution

2020-10-12