Regular Expressions 101

Pro

^start of line

Non-Capturing Group(?:(?:1?[1-9]?\d|[12][0-4]\d|25[0-5])(?:\.(?!$)|$)){4}

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

Non-Capturing Group(?:1?[1-9]?\d|[12][0-4]\d|25[0-5])

1st Alternative1?[1-9]?\d

1?optionally matches the literal 1 (49₁₀ / 61₈ / 31₁₆)

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

2nd Alternative[12][0-4]\d

Character Class[12]

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

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)

Non-Capturing Group(?:\.(?!$)|$)

1st Alternative\.(?!$)

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Negative Lookahead(?!$)

$end of line

2nd Alternative$

$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

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

New

123.1.2.3
123.1.1.1.1
266.1.1
00.1.1.1
1234.1.1.1

123.1.2.3
123.1.1.1.1
266.1.1
00.1.1.1
1234.1.1.1