Regular Expressions 101

httpthe literal text http (case insensitive)

s?optionally matches the literal s (115₁₀ / 163₈ / 73₁₆) (case insensitive)

:// the literal text ://

Non-Capturing Group(?:www\.)?

?repeats the group contents below at most once:

wwwthe literal text www (case insensitive)

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

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

Non-Capturing Group(?:[a-z][a-z0-9-]*[a-z0-9]\.|[a-z]\.)+

+repeats the group contents below at least once:

1st Alternative[a-z][a-z0-9-]*[a-z0-9]\.

Character Class[a-z]

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

Character Class[a-z0-9-]*

*matches any number of characters from the set below:

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

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 insensitive)

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

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

2nd Alternative[a-z]\.

Character Class[a-z]

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

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Non-Capturing Group(?:[a-z][a-z0-9-]*[a-z0-9]|[a-z])

1st Alternative[a-z][a-z0-9-]*[a-z0-9]

Character Class[a-z]

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

Character Class[a-z0-9-]*

*matches any number of characters from the set below:

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

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 insensitive)

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

2nd Alternative[a-z]

Character Class[a-z]

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

Global pattern flags

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

i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters

x modifier: extended. Ignores unescaped whitespace and comments outside character classes

x

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Search reference

Regular Expression

https?://
(?:www\.)?
((?:[a-z][a-z0-9-]*[a-z0-9]\.|[a-z]\.)+
 (?:[a-z][a-z0-9-]*[a-z0-9]|[a-z]))

Unit Tests

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