Regular Expressions 101

Pro

^start of line

Negative Lookahead(?!.*(?:[a-z][0-9]|[0-9][a-z]))

.*any character (except for line terminators), repeated any number of times

Non-Capturing Group(?:[a-z][0-9]|[0-9][a-z])

1st Alternative[a-z][0-9]

Character Class[a-z]

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

Character Class[0-9]

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

2nd Alternative[0-9][a-z]

Character Class[0-9]

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

Character Class[a-z]

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

Negative Lookahead(?!.*?\.\.)

.*?any character (except for line terminators), repeated any number of times

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

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 . (46₁₀ / 56₈ / 2E₁₆)

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

\da digit

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

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 . (46₁₀ / 56₈ / 2E₁₆)

$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

Detailed match information will be displayed here automatically.

25 tokens

^(?!.*(?:[a-z][0-9]|[0-9][a-z]))(?!.*?\.\.)[a-z0-9.]*\.\d\.[a-z0-9.]*$

aha.comment.1.app
aha.comment1.app

a.1.b.c.d.2.a
.a.1.b.c.d.2.a.
a.2.b.c2.a.1.
a.a
a..1.1....