Regular Expressions 101

^start of line

Positive Lookahead(?=.*[A-Za-z].*[A-Za-z])

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

Character Class[A-Za-z]

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

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

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

Character Class[A-Za-z]

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

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

Group 1([A-Za-z0-9]((?!.*[\._]{2})([\w\d\.]{1,23}))[A-Za-z0-9])

Character Class[A-Za-z0-9]

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)

Group 2((?!.*[\._]{2})([\w\d\.]{1,23}))

Negative Lookahead(?!.*[\._]{2})

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

Character Class[\._]{2}

{2}matches exactly 2 characters from the set below:

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

Group 3([\w\d\.]{1,23})

Character Class[\w\d\.]{1,23}

{1,23}matches between 1 and 23 characters from the set below:

\wany word character

\da digit

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Character Class[A-Za-z0-9]

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)

$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.

25 tokens

Regular Expression

^(?=.*[A-Za-z].*[A-Za-z])([A-Za-z0-9]((?!.*[\._]{2})([\w\d\.]{1,23}))[A-Za-z0-9])$

New

A.s
0as
a.a
a.0
0.0
a._a
a.0a
1rockit.man
q3w
e4.45r.d.2
sp_am
.ret.
123
12a
ret..wer
super_.duper
_petrat or petrat_

A.s
0as
a.a
a.0
0.0
a._a
a.0a
1rockit.man
q3w
e4.45r.d.2
sp_am
.ret.
123
12a
ret..wer
super_.duper
_petrat or petrat_