Regular Expressions 101

^start of string

Non-Capturing Group(?:(?:[1-9]?[0-9]|1[0-9][0-9]|2(?:[0-4][0-9]|5[0-5]))\.){3}

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

Non-Capturing Group(?:[1-9]?[0-9]|1[0-9][0-9]|2(?:[0-4][0-9]|5[0-5]))

1st Alternative[1-9]?[0-9]

Character Class[1-9]?

?matches at most one character from the set below:

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

Character Class[0-9]

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

2nd Alternative1[0-9][0-9]

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

Character Class[0-9]

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

Character Class[0-9]

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

3rd Alternative2(?:[0-4][0-9]|5[0-5])

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

Non-Capturing Group(?:[0-4][0-9]|5[0-5])

1st Alternative[0-4][0-9]

Character Class[0-4]

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

Character Class[0-9]

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

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(?:[1-9]?[0-9]|1[0-9][0-9]|2(?:[0-4][0-9]|5[0-5]))

1st Alternative[1-9]?[0-9]

Character Class[1-9]?

?matches at most one character from the set below:

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

Character Class[0-9]

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

2nd Alternative1[0-9][0-9]

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

Character Class[0-9]

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

Character Class[0-9]

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

3rd Alternative2(?:[0-4][0-9]|5[0-5])

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

Non-Capturing Group(?:[0-4][0-9]|5[0-5])

1st Alternative[0-4][0-9]

Character Class[0-4]

Character Class[0-9]

2nd Alternative5[0-5]

Non-Capturing Group(?:\/(?:[12]?[0-9]|3[0-2]))?

$end of string

Detailed match information will be displayed here automatically.

Search reference

Regular Expression

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

New

172.0.0.1/16