Regular Expressions 101

^start of line

Positive Lookahead(?=\S{8})

\S{8}any non-whitespace character, repeated exactly 8 times

Negative Lookahead(?!\S*@\S*\.\S*\.)

\S*any non-whitespace character, repeated any number of times

@the literal @ (64₁₀ / 100₈ / 40₁₆)

\S*any non-whitespace character, repeated any number of times

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

\S*any non-whitespace character, repeated any number of times

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Character Class[a-zA-Z]

a-zone character from a (97₁₀) to z (122₁₀) (case sensitive)

A-Zone character from A (65₁₀) to Z (90₁₀) (case sensitive)

\S*any non-whitespace character, repeated any number of times

Non-Capturing Group(?:@\S+\.\S+)?

?repeats the group contents below at most once:

@the literal @ (64₁₀ / 100₈ / 40₁₆)

\S+any non-whitespace character, repeated at least once

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

\S+any non-whitespace character, repeated at least once

$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

^(?=\S{8})(?!\S*@\S*\.\S*\.)[a-zA-Z]\S*(?:@\S+\.\S+)?$

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