regex101: Ipv4 validation

Pro

Group 1(^([1-9][\d]?|1[\d]?[\d]?|2[0-4][\d]|25[0-5])\.)

^start of line

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

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

Character Class[1-9]

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

Character Class[\d]?

?matches at most one character from the set below:

\da digit

2nd Alternative1[\d]?[\d]?

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

Character Class[\d]?

?matches at most one character from the set below:

\da digit

Character Class[\d]?

?matches at most one character from the set below:

\da digit

3rd Alternative2[0-4][\d]

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

Character Class[0-4]

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

Character Class[\d]

\da digit

4th Alternative25[0-5]

25the literal text 25

Character Class[0-5]

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

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

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

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

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

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

1st Alternative0

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

2nd Alternative[1-9][0-9]?

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)

3rd Alternative1[\d]?[\d]?

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

Character Class[\d]?

?matches at most one character from the set below:

\da digit

Character Class[\d]?

?matches at most one character from the set below:

\da digit

4th Alternative2[0-4][\d]

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

Character Class[0-4]

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

Character Class[\d]

5th Alternative25[0-5]

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Group 6(0|[1-9][\d]?|1[\d]?[\d]?|2[0-4][\d]|25[0-5])

$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

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

Unit Tests

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