Regular Expressions 101

Explanation

Pro

Non-Capturing Group(?:^(\w{1,255}):(.{1,255})@|^)

1st Alternative^(\w{1,255}):(.{1,255})@

^start of line

Group 1(\w{1,255})

\w{1,255}a Unicode word character, repeated between 1 and 255 times

:the literal : (58₁₀ / 72₈ / 3A₁₆)

Group 2(.{1,255})

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

@the literal @ (64₁₀ / 100₈ / 40₁₆)

2nd Alternative^

^start of line

Non-Capturing Group(?:(?:(?=\S{0,253}(?:$|:| ))((?:[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?\.)+(?:[a-z0-9]{1,63})))|localhost)

1st Alternative(?:(?=\S{0,253}(?:$|:| ))((?:[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?\.)+(?:[a-z0-9]{1,63})))

Non-Capturing Group(?:(?=\S{0,253}(?:$|:| ))((?:[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?\.)+(?:[a-z0-9]{1,63})))

Positive Lookahead(?=\S{0,253}(?:$|:| ))

\S{0,253}any character that is not Unicode whitespace, repeated between 0 and 253 times

Non-Capturing Group(?:$|:| )

1st Alternative$

$end of line

2nd Alternative:

:the literal : (58₁₀ / 72₈ / 3A₁₆)

3rd Alternative

the literal (32₁₀ / 40₈ / 20₁₆)

Group 3((?:[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?\.)+(?:[a-z0-9]{1,63}))

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

+repeats the group contents below at least once:

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)

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

?repeats the group contents below at most once:

Character Class[a-z0-9-]{0,61}

{0,61}matches between 0 and 61 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)

Non-Capturing Group(?:[a-z0-9]{1,63})

Character Class[a-z0-9]{1,63}

{1,63}matches between 1 and 63 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)

2nd Alternativelocalhost

localhostthe literal text localhost (case insensitive)

Group 4(:\d{1,5})?

?repeats the group contents below at most once:

:the literal : (58₁₀ / 72₈ / 3A₁₆)

\d{1,5}a Unicode decimal digit, repeated between 1 and 5 times

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

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

Match Information

Detailed match information will be displayed here automatically.

Quick Reference

25 tokens

Regular Expression

(?:^(\w{1,255}):(.{1,255})@|^)(?:(?:(?=\S{0,253}(?:$|:| ))((?:[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?\.)+(?:[a-z0-9]{1,63})))|localhost)(:\d{1,5})?

New

Valid localhost addresses:
localhost
user:password@localhost:80
localhost:8080/path/to/page.html


Valid IPv4 addresses:
10.10.0.1 
192.168.0.1 
192.168.0.1:8888 
user:password@192.168.0.1:8888 
user:password@192.168.0.1


Valid IPv6 addresses: // regex does not check for that, check here: http://vernon.mauery.com/content/projects/linux/ipv6_regex

100::
100::ffff:ffff:ffff:ffff
::ffff:0.0.0.0
64:ff9b::0.0.0.0
ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff
fe80::
2001:2f:ffff:ffff:ffff:ffff:ffff:ffff
2001:db8::
::1


Valid domains: // all should work
www.test.com
www1.test.com
www1.test.com:8080    
test.com
test-test.com
test.com/path/to/page?var=1&var2=2
test.com:80
user:password@test.com
user:password@test-test.com
user:password@test.com/path/to/page
user:password@test.com/path/to/page?var=1&var2=2
user:password@test.com:80
user:password@test.com:80/path/to/page?var=1&var2=2
Maximum-Length-Of-63-Characters-For-A-Subdomain-Completely-Used.com
user:password@Maximum-Length-Of-63-Characters-Fo