Regular Expressions 101

^start of line

Negative Lookahead(?!.*(?:[_-]$|_ | _))

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

Non-Capturing Group(?:[_-]$|_ | _)

1st Alternative[_-]$

Character Class[_-]

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

-the literal - (45₁₀ / 55₈ / 2D₁₆)

$end of line

2nd Alternative_

_ the literal text _

3rd Alternative _

_the literal text _

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[\w -]*

*matches any number of characters from the set below:

\wany word character

the literal (32₁₀ / 40₈ / 20₁₆)

-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

Detailed match information will be displayed here automatically.

Search reference

Regular Expression

^(?!.*(?:[_-]$|_ | _))[a-zA-Z][\w -]*$

New

 // Match
HelloWorld
Hello_World
Hello_World_1
He110_W0rld
Hello - World
Hello-World

 // doesn't match
Hello _World
Hello_ World
Hello _ World
_HelloWorld