Regular Expressions 101

Pro

^start of line

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

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

\-the literal - (45₁₀ / 55₈ / 2D₁₆)

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

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

\-the literal - (45₁₀ / 55₈ / 2D₁₆)

.+any character (except for line terminators), repeated at least once

\-the literal - (45₁₀ / 55₈ / 2D₁₆)

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

\-the literal - (45₁₀ / 55₈ / 2D₁₆)

Negative Lookahead(?!-)

-the literal - (45₁₀ / 55₈ / 2D₁₆)

Character Class[a-z0-9-]{0,52}

{0,52}matches between 0 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)

Negative Lookbehind(?<!-)

-the literal - (45₁₀ / 55₈ / 2D₁₆)

$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

Regular Expression

^(?!.*\-\-)(?!.*\-.+\-.*\-)(?!-)[a-z0-9-]{0,52}(?<!-)$

New

MycatBilly-Bobhas9lives
nlyallows52total
-thisshouldnotmatch
norshouldthis-
thisis--anotherbaddie
nothing-wrong-here
but-this-is-anono
thisistoolongfartoolongtomeetthemaximumlengthrequirement

Substitution

MycatBilly-Bobhas9lives
nlyallows52total
-thisshouldnotmatch
norshouldthis-
thisis--anotherbaddie
nothing-wrong-here
but-this-is-anono
thisistoolongfartoolongtomeetthemaximumlengthrequirement