Regular Expressions 101

^start of line

Character Class[a-zA-Z]

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

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

Character Class[a-zA-Z0-9_]{3,24}

{3,24}matches between 3 and 24 characters from the set below:

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

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

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

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

$end of line

Negative Lookbehind(?<!_)

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

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

Regular Expression

^[a-zA-Z][a-zA-Z0-9_]{3,24}$(?<!_)

New

The username is between 4 and 25 characters.
It must start with a letter.
It can only contain letters, numbers, and the underscore character.
It cannot end with an underscore character.

Extraction

The username is between 4 and 25 characters.
It must start with a letter.
It can only contain letters, numbers, and the underscore character.
It cannot end with an underscore character.