Regular Expressions 101

Positive Lookbehind(?<=(?<!\S)(?:hello|hi)\s+)

Negative Lookbehind(?<!\S)

\Sany non-whitespace character

Non-Capturing Group(?:hello|hi)

1st Alternativehello

hellothe literal text hello (case sensitive)

2nd Alternativehi

hithe literal text hi (case sensitive)

\s+any whitespace character, repeated at least once

worldthe literal text world (case sensitive)

Positive Lookahead(?=\s*[!?.](?!\S))

\s*any whitespace character, repeated any number of times

Character Class[!?.]

!the literal ! (33₁₀ / 41₈ / 21₁₆)

?the literal ? (63₁₀ / 77₈ / 3F₁₆)

.the literal . (46₁₀ / 56₈ / 2E₁₆)

Negative Lookahead(?!\S)

\Sany non-whitespace character

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

Regular Expression

(?<=(?<!\S)(?:hello|hi)\s+)world(?=\s*[!?.](?!\S))

New

hello world!

hello world!x

$hello world!

hello world!

hello world!x

$hello world!