Regular Expressions 101

Positive Lookbehind(?<=\s|^)

1st Alternative\s

\sany whitespace character

2nd Alternative^

^start of string

Group 1([A-Za-z0-9]+[._-]?[A-Za-z0-9]+)+

+repeats the group contents below at least once:

Character Class[A-Za-z0-9]+

+matches at least one character from the set below:

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

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

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

Character Class[._-]?

?matches at most one character from the set below:

.the literal . (46₁₀ / 56₈ / 2E₁₆)

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

-the literal - (45₁₀ / 55₈ / 2D₁₆)

Character Class[A-Za-z0-9]+

+matches at least one character from the set below:

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

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

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

@the literal @ (64₁₀ / 100₈ / 40₁₆)

Group 2([A-Za-z]+[._-]?)+

+repeats the group contents below at least once:

Character Class[A-Za-z]+

+matches at least one character from the set below:

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

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

Character Class[._-]?

?matches at most one character from the set below:

.the literal . (46₁₀ / 56₈ / 2E₁₆)

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

-the literal - (45₁₀ / 55₈ / 2D₁₆)

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Character Class[A-Za-z]+

+matches at least one character from the set below:

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

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

\ban ASCII word boundary

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

Detailed match information will be displayed here automatically.

Search reference

Regular Expression

(?<=\s|^)([A-Za-z0-9]+[._-]?[A-Za-z0-9]+)+@([A-Za-z]+[._-]?)+\.[A-Za-z]+\b

New

VALID: info@softuni-bulgaria.org, kiki@hotmail.uk, no-reply@github.com,
s.peterson@mail.uu.net, info-bg@software-university.software.academy.
vlad@abg.bg

INVALID: --123@gmail.com, …@mail.bg, .info@info.info, _steve@yahoo.cn,
mike@helloworld, mike@.unknown.soft., s.johnson@invalid-.