Regular Expressions 101

Explanation

Pro

Positive Lookahead(?=^[A-Za-z0-9]+\s?[A-Za-z0-9]+$)

^start of line

Character Class[A-Za-z0-9]+

+matches at least one character from the set below:

A-Zone character from A (65₁₀) to Z (90₁₀) (case sensitive)

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

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

\s?optionally matches any whitespace character

Character Class[A-Za-z0-9]+

+matches at least one character from the set below:

A-Zone character from A (65₁₀) to Z (90₁₀) (case sensitive)

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

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

$end of line

.{3,30}any character (except for line terminators), repeated between 3 and 30 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

Detailed match information will be displayed here automatically.

26 tokens

(?=^[A-Za-z0-9]+\s?[A-Za-z0-9]+$).{3,30}

New

username123
user name 123
user name123
u sername123
 username123

username123
user name 123
user name123
u sername123
 username123