Regular Expressions 101

\Bnot an ASCII word boundary

Non-Capturing Group(?:(?=(?:\d{3})+\.)|(?!.*\.)(?<!\..*)(?=(?:\d{3})+$))

1st Alternative(?=(?:\d{3})+\.)

Positive Lookahead(?=(?:\d{3})+\.)

Non-Capturing Group(?:\d{3})+

+repeats the group contents below at least once:

\d{3}a digit, repeated exactly 3 times

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

2nd Alternative(?!.*\.)(?<!\..*)(?=(?:\d{3})+$)

Negative Lookahead(?!.*\.)

.*any character (except for line terminators), repeated any number of times

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Negative Lookbehind(?<!\..*)

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

.*any character (except for line terminators), repeated any number of times

Positive Lookahead(?=(?:\d{3})+$)

Non-Capturing Group(?:\d{3})+

+repeats the group contents below at least once:

\d{3}a digit, repeated exactly 3 times

$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

Detailed match information will be displayed here automatically.

Search reference

Regular Expression

\B(?:(?=(?:\d{3})+\.)|(?!.*\.)(?<!\..*)(?=(?:\d{3})+$))

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1234.5678
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1234567.89012
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