regex101: IPv4 non zero first and last octet

Pro

^start of line

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

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 Alternative0?[1-9][0-9]?

0?optionally matches the literal 0 (48₁₀ / 60₈ / 30₁₆)

Character Class[1-9]

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

Character Class[0-9]?

?matches at most one character from the set below:

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

5th Alternative0?[0-9]?[1-9]

0?optionally matches the literal 0 (48₁₀ / 60₈ / 30₁₆)

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)

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

{2}repeats the group contents below exactly 2 times:

.any character (except for line terminators)

Group 3(25[0-5]|2[0-4][0-9]|[0-1]?[0-9]?[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 Alternative[0-1]?[0-9]?[0-9]

Character Class[0-1]?

?matches at most one character from the set below:

0-1one character from 0 (48₁₀) to 1 (49₁₀)

Character Class[0-9]?

?matches at most one character from the set below:

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

Character Class[0-9]

.any character (except for line terminators)

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

$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

25 tokens

Regular Expression

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

New

256.256.256.256
256.255.255.255
255.256.255.255
255.255.256.255
255.255.255.256
255.255.255.255
255.255.255.0
1.1.1.1
0.1.1.1
1.0.1.1
1.1.0.1
1.0.0.1
1.0.0.0
0.0.0.0

Substitution

256.256.256.256
256.255.255.255
255.256.255.255
255.255.256.255
255.255.255.256
255.255.255.255
255.255.255.0
1.1.1.1
0.1.1.1
1.0.1.1
1.1.0.1
1.0.0.1
1.0.0.0
0.0.0.0