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)

Group 1([a-zA-Z0-9]|(_(?!_)))+

+repeats the group contents below at least once:

1st Alternative[a-zA-Z0-9]

Character Class[a-zA-Z0-9]

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)

2nd Alternative(_(?!_))

Group 2(_(?!_))

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

Negative Lookahead(?!_)

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

Character Class[a-zA-Z0-9]

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)

$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.

Search reference

Regular Expression

^[a-zA-Z]([a-zA-Z0-9]|(_(?!_)))+[a-zA-Z0-9]$

New

as23142
as231 qwdcasd
asdc_sdcsad
asd_
asd__scsd