Regular Expressions 101

Pro

^start of line

Positive Lookahead(?=[a-z0-9-]{1,52}$)

Character Class[a-z0-9-]{1,52}

{1,52}matches between 1 and 52 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)

$end of line

Character Class[a-z0-9]+

+matches at least one character from the set below:

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]+){0,2}

{0,2}repeats the group contents below between 0 and 2 times:

-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 insensitive)

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

$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

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

Detailed match information will be displayed here automatically.

25 tokens

^(?=[a-z0-9-]{1,52}$)[a-z0-9]+(?:-[a-z0-9]+){0,2}$

New

abc-123
abc-123-abc

-abc-123
abc-123-
abc-123-abc-123
abc-12#-abc

abc-123
abc-123-abc

-abc-123
abc-123-
abc-123-abc-123
abc-12#-abc