regex101: PCRE2 (PHP) Match Workspace

^start of line

Positive Lookahead(?=.{3,16}$)

.{3,16}any character (except for line terminators), repeated between 3 and 16 times

$end of line

Character Class[a-z]

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

Group 1([0-9a-z]|[0-9a-z\-](?=[0-9a-z])){1,}

{1,}repeats the group contents below at least once:

1st Alternative[0-9a-z]

Character Class[0-9a-z]

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

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

2nd Alternative[0-9a-z\-](?=[0-9a-z])

Character Class[0-9a-z\-]

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

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

\-the literal - (45₁₀ / 55₈ / 2D₁₆)

Positive Lookahead(?=[0-9a-z])

Character Class[0-9a-z]

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

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

Group 2([\.](?=[a-z][0-9a-z\-][0-9a-z\-])[a-z]([0-9a-z]|[0-9a-z\-](?=[0-9a-z])){1,}){0,}

{0,}repeats the group contents below any number of times:

Character Class[\.]

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Positive Lookahead(?=[a-z][0-9a-z\-][0-9a-z\-])

Character Class[a-z]

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

Character Class[0-9a-z\-]

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

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

\-the literal - (45₁₀ / 55₈ / 2D₁₆)

Character Class[0-9a-z\-]

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

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

\-the literal - (45₁₀ / 55₈ / 2D₁₆)

Character Class[a-z]

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

Group 3([0-9a-z]|[0-9a-z\-](?=[0-9a-z])){1,}

{1,}repeats the group contents below at least once:

1st Alternative[0-9a-z]

Character Class[0-9a-z]

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

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

2nd Alternative[0-9a-z\-](?=[0-9a-z])

Character Class[0-9a-z\-]

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

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

\-the literal - (45₁₀ / 55₈ / 2D₁₆)

Positive Lookahead(?=[0-9a-z])

Character Class[0-9a-z]

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

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

$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

Search reference

Regular Expression

^(?=.{3,16}$)[a-z]([0-9a-z]|[0-9a-z\-](?=[0-9a-z])){1,}([\.](?=[a-z][0-9a-z\-][0-9a-z\-])[a-z]([0-9a-z]|[0-9a-z\-](?=[0-9a-z])){1,}){0,}$

Unit Tests

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