Regular Expressions 101

^start of line

Group 1(0?[0-9]{0,4}(?:\.\d+)?|1\d{4}(?:\.\d+)?|20[0-4][0-7][0-8](?:\.\d+)?|20479(?:\.[0-7])?)

1st Alternative0?[0-9]{0,4}(?:\.\d+)?

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

Character Class[0-9]{0,4}

{0,4}matches between 0 and 4 characters from the set below:

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

Non-Capturing Group(?:\.\d+)?

?repeats the group contents below at most once:

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

\d+a digit, repeated at least once

2nd Alternative1\d{4}(?:\.\d+)?

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

\d{4}a digit, repeated exactly 4 times

Non-Capturing Group(?:\.\d+)?

?repeats the group contents below at most once:

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

\d+a digit, repeated at least once

3rd Alternative20[0-4][0-7][0-8](?:\.\d+)?

20the literal text 20

Character Class[0-4]

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

Character Class[0-7]

0-7one character from 0 (48₁₀) to 7 (55₁₀)

Character Class[0-8]

0-8one character from 0 (48₁₀) to 8 (56₁₀)

Non-Capturing Group(?:\.\d+)?

?repeats the group contents below at most once:

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

\d+a digit, repeated at least once

4th Alternative20479(?:\.[0-7])?

20479the literal text 20479

Non-Capturing Group(?:\.[0-7])?

?repeats the group contents below at most once:

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Character Class[0-7]

0-7one character from 0 (48₁₀) to 7 (55₁₀)

$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

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Search reference

Regular Expression

^(0?[0-9]{0,4}(?:\.\d+)?|1\d{4}(?:\.\d+)?|20[0-4][0-7][0-8](?:\.\d+)?|20479(?:\.[0-7])?)$

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