Regular Expressions 101

Explanation

Pro

\ban ASCII word boundary

Non-Capturing Group(?:(?:\d{1,2}|1\d{2}|2(?:[0-4]\d|5[0-5]))\.){3}

{3}repeats the group contents below exactly 3 times:

Non-Capturing Group(?:\d{1,2}|1\d{2}|2(?:[0-4]\d|5[0-5]))

1st Alternative\d{1,2}

\d{1,2}a digit, repeated between 1 and 2 times

2nd Alternative1\d{2}

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

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

3rd Alternative2(?:[0-4]\d|5[0-5])

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

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

1st Alternative[0-4]\d

Character Class[0-4]

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

\da digit

2nd Alternative5[0-5]

5the literal 5 (53₁₀ / 65₈ / 35₁₆)

Character Class[0-5]

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

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Non-Capturing Group(?:\d{1,2}|1\d{2}|2(?:[0-4]\d|5[0-5]))

1st Alternative\d{1,2}

\d{1,2}a digit, repeated between 1 and 2 times

2nd Alternative1\d{2}

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

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

3rd Alternative2(?:[0-4]\d|5[0-5])

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

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

1st Alternative[0-4]\d

Character Class[0-4]

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

\da digit

2nd Alternative5[0-5]

5the literal 5 (53₁₀ / 65₈ / 35₁₆)

Character Class[0-5]

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

\ban ASCII word boundary

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

Match Information

Detailed match information will be displayed here automatically.

Quick Reference

26 tokens

Regular Expression

\b(?:(?:\d{1,2}|1\d{2}|2(?:[0-4]\d|5[0-5]))\.){3}(?:\d{1,2}|1\d{2}|2(?:[0-4]\d|5[0-5]))\b

IP: 128.1.1.0
Bad IP: 256.12.34.33
Good IP: 255.12.34.33

Substitution

IP: 128.1.1.0
Bad IP: 256.12.34.33
Good IP: 255.12.34.33