Regular Expressions 101

Pro

^start of line

Group 1((1\d{2}|2[0-4]\d|25[0-5]|[1-9]?\d)(\.(?=\d)|(?!\d))){4}

{4}repeats the group contents below exactly 4 times:

Group 2(1\d{2}|2[0-4]\d|25[0-5]|[1-9]?\d)

1st Alternative1\d{2}

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

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

2nd Alternative2[0-4]\d

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

Character Class[0-4]

0-4one character from 0 (48₁₀) to 4 (52₁₀)

\da Unicode decimal digit

3rd Alternative25[0-5]

25the literal text 25

Character Class[0-5]

0-5one character from 0 (48₁₀) to 5 (53₁₀)

4th Alternative[1-9]?\d

Character Class[1-9]?

?matches at most one character from the set below:

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

\da Unicode decimal digit

Group 3(\.(?=\d)|(?!\d))

1st Alternative\.(?=\d)

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Positive Lookahead(?=\d)

\da Unicode decimal digit

2nd Alternative(?!\d)

Negative Lookahead(?!\d)

\da Unicode decimal digit

Group 4(/([12]?\d|3[0-2]))?

?repeats the group contents below at most once:

/the literal / (47₁₀ / 57₈ / 2F₁₆)

Group 5([12]?\d|3[0-2])

1st Alternative[12]?\d

Character Class[12]?

?matches at most one character from the set below:

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

\da Unicode decimal digit

2nd Alternative3[0-2]

3the literal 3 (51₁₀ / 63₈ / 33₁₆)

Character Class[0-2]

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

$end of line

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

^((1\d{2}|2[0-4]\d|25[0-5]|[1-9]?\d)(\.(?=\d)|(?!\d))){4}(/([12]?\d|3[0-2]))?$

New

10.238.51.19
12.89.119.255/30
12.89.119.25
1.2.3.4/24
0.0.0.0/0

00.00.00.00
0.0.0.0.0
1.1..123
1.1.1234.123
1.1.1.123/
1.1.456.78