Regular Expressions 101

Explanation

Pro

^start of string

Group 1((([a-z0-9][a-z0-9\-]*[a-z0-9])|[a-z0-9]+)\.)*

*repeats the group contents below any number of times:

Group 2(([a-z0-9][a-z0-9\-]*[a-z0-9])|[a-z0-9]+)

1st Alternative([a-z0-9][a-z0-9\-]*[a-z0-9])

Group 3([a-z0-9][a-z0-9\-]*[a-z0-9])

Character Class[a-z0-9]

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

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

Character Class[a-z0-9\-]*

*matches any number of characters from the set below:

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

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

\-the literal - (45₁₀ / 55₈ / 2D₁₆)

Character Class[a-z0-9]

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

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

2nd Alternative[a-z0-9]+

Character Class[a-z0-9]+

+matches at least one character from the set below:

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

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

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Group 4([a-z]+|xn\-\-[a-z0-9]+)

1st Alternative[a-z]+

Character Class[a-z]+

+matches at least one character from the set below:

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

2nd Alternativexn\-\-[a-z0-9]+

xnthe literal text xn (case sensitive)

\-the literal - (45₁₀ / 55₈ / 2D₁₆)

Character Class[a-z0-9]+

+matches at least one character from the set below:

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

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

\.?optionally matches the literal . (46₁₀ / 56₈ / 2E₁₆)

$end of string, or before its final line terminator

Ready to run

25 tokens

^((([a-z0-9][a-z0-9\-]*[a-z0-9])|[a-z0-9]+)\.)*([a-z]+|xn\-\-[a-z0-9]+)\.?$