Regular Expressions 101

Explanation

Pro

^start of line

\ban ASCII word boundary

Group 1(0|[1-9][0-9]{0,3}|[1-5][0-9]{4}|6[0-4][0-9]{3}|65[0-4][0-9]{2}|655[0-2][0-9]|6553[0-5])

1st Alternative0

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

2nd Alternative[1-9][0-9]{0,3}

Character Class[1-9]

1-9one character from 1 (49₁₀) to 9 (57₁₀)

Character Class[0-9]{0,3}

{0,3}matches between 0 and 3 characters from the set below:

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

3rd Alternative[1-5][0-9]{4}

Character Class[1-5]

1-5one character from 1 (49₁₀) to 5 (53₁₀)

Character Class[0-9]{4}

{4}matches exactly 4 characters from the set below:

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

4th Alternative6[0-4][0-9]{3}

6the literal 6 (54₁₀ / 66₈ / 36₁₆)

Character Class[0-4]

0-4one character from 0 (48₁₀) to 4 (52₁₀)

Character Class[0-9]{3}

{3}matches exactly 3 characters from the set below:

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

5th Alternative65[0-4][0-9]{2}

65the literal text 65

Character Class[0-4]

0-4one character from 0 (48₁₀) to 4 (52₁₀)

Character Class[0-9]{2}

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

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

6th Alternative655[0-2][0-9]

655the literal text 655

Character Class[0-2]

0-2one character from 0 (48₁₀) to 2 (50₁₀)

Character Class[0-9]

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

7th Alternative6553[0-5]

6553the literal text 6553

Character Class[0-5]

0-5one character from 0 (48₁₀) to 5 (53₁₀)

\ban ASCII word boundary

\hany horizontal whitespace character

Group 2(\.|\b((?=.{1,255}$)(?:xn\-\-)?(?!-)(?!.*--)[a-z0-9]([a-z0-9-]{0,61}[a-z0-9])?(?:\.[a-z0-9]([a-z0-9-]{0,61}[a-z0-9])?)*\.?)\b)

1st Alternative\.

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

2nd Alternative\b((?=.{1,255}$)(?:xn\-\-)?(?!-)(?!.*--)[a-z0-9]([a-z0-9-]{0,61}[a-z0-9])?(?:\.[a-z0-9]([a-z0-9-]{0,61}[a-z0-9])?)*\.?)\b

\ban ASCII word boundary

Group 3((?=.{1,255}$)(?:xn\-\-)?(?!-)(?!.*--)[a-z0-9]([a-z0-9-]{0,61}[a-z0-9])?(?:\.[a-z0-9]([a-z0-9-]{0,61}[a-z0-9])?)*\.?)

Positive Lookahead(?=.{1,255}$)

.{1,255}any character (except for line terminators), repeated between 1 and 255 times

$end of line

Non-Capturing Group(?:xn\-\-)?

?repeats the group contents below at most once:

xnthe literal text xn (case sensitive)

\-the literal - (45₁₀ / 55₈ / 2D₁₆)

\-the literal - (45₁₀ / 55₈ / 2D₁₆)

Negative Lookahead(?!-)

Negative Lookahead(?!.*--)

Character Class[a-z0-9]

Group 4([a-z0-9-]{0,61}[a-z0-9])?

Non-Capturing Group(?:\.[a-z0-9]([a-z0-9-]{0,61}[a-z0-9])?)*

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

\ban ASCII word boundary

Non-Capturing Group(?:\.)?

Negative Lookahead(?!=)

Group 6(\h(([a-z0-9-]{1,63})((\=\")[\x21\x23-\x27\x2A-\x3A\x3C-\x7E]{1,255}+(\"))?)?)*?

$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

Match Information

Detailed match information will be displayed here automatically.

Quick Reference

25 tokens

Regular Expression

^\b(0|[1-9][0-9]{0,3}|[1-5][0-9]{4}|6[0-4][0-9]{3}|65[0-4][0-9]{2}|655[0-2][0-9]|6553[0-5])\b\h(\.|\b((?=.{1,255}$)(?:xn\-\-)?(?!-)(?!.*--)[a-z0-9]([a-z0-9-]{0,61}[a-z0-9])?(?:\.[a-z0-9]([a-z0-9-]{0,61}[a-z0-9])?)*\.?)\b)(?:\.)?(?!=)(\h(([a-z0-9-]{1,63})((\=\")[\x21\x23-\x27\x2A-\x3A\x3C-\x7E]{1,255}+(\"))?)?)*?$

New

230 example.com
56 subsubdomain.subdomain.example.com.thisisaverylongdomainnamewithseventycharacters
89 subsubdomain.subdomain.example.com.thisisaverylongdomainnamewithseventycharacters test
1 gOOglE.com alpn="h3,h2"
250 exmpla.com test="test"
250 exmpla.com 33="3.63"
250 . 33="363"
1 . alpn="h3,h2"
1 example.com. alpn="h3,h2"
2 . test=test
3 . test=""
1 . alpn="h3,h2" ipv4hint="192.0.2.1" ipv6hint="2001:db8::1"
1 . alpn="h3,h2" ipv4hi-nt="192.0.2.1" ipv6hint="2001:db8::1"
1 test.org alpn="h3,h2" ipv4hi-nt="192.0.2.1" ipv6hint="2001:db8::1"
1 test.org alpn="h3,h2" ipv4hi-nt="192.0.2.1" ipv6hint="2001:db8::1" ipv4hi-nt="192.0.2.1" ipv6hint="2001:db8::1" ipv4hi-nt="192.0.2.1" ipv6hint="2001:db8::1" ipv4hi-nt="192.0.2.1" ipv6hint="2001:db8::1" ipv4hi-nt="192.0.2.1" ipv6hint="2001:db8::1"
1 test.org alpnfeefefefefefwefwefwefwefwefwefwefwefwefwefwefwefhththegerg="h3,h2"
1 test.org alpnfeefefefefefwefweefwefwefwefwefwefwefwefwefhththegerg="h3\,h2"
1 test.org test="jn7j64m764mi67i4i467nhin0iu