regex101: ipv4 addresses

Pro

Group 1((25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9]?[0-9])\.){3}

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

Group 2(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9]?[0-9])

1st Alternative25[0-5]

25the literal text 25

Character Class[0-5]

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

2nd Alternative2[0-4][0-9]

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

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)

3rd 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)

4th 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)

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Group 3(25[0-4]|2[0-4][0-9]|1[0-9][0-9]|[0-9]?[1-9])

1st Alternative25[0-4]

25the literal text 25

Character Class[0-4]

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

2nd Alternative2[0-4][0-9]

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

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)

3rd 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)

4th Alternative[0-9]?[1-9]

Character Class[0-9]?

?matches at most one character from the set below:

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

Character Class[1-9]

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

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

25 tokens

Regular Expression

((25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9]?[0-9])\.){3}(25[0-4]|2[0-4][0-9]|1[0-9][0-9]|[0-9]?[1-9])

New

192.168.1.1
8.8.8.8
9.9.9.9
127.0.0.1
255.255.255.255 # can't end in 255, reserved for broadcast
0.0.0.0 # can't end in 0, i don't know what that's reserved for
0.0.0.1

Substitution

192.168.1.1
8.8.8.8
9.9.9.9
127.0.0.1
255.255.255.255 # can't end in 255, reserved for broadcast
0.0.0.0 # can't end in 0, i don't know what that's reserved for
0.0.0.1