Regular Expressions 101

^start of line

Non-Capturing Group(?:\w*[a-zA-Z_]\w*)?

?repeats the group contents below at most once:

\w*a Unicode word character, repeated any number of times

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)

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

\w*a Unicode word character, repeated any number of times

$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

^(?:\w*[a-zA-Z_]\w*)?$

New

expression123
123expression
exp123ression

1235234567544
expression$123