Regex Lookarounds

Lookarounds are used to match a pattern only if it is followed or preceded by another pattern. They are zero-width assertions, which means they don’t consume any characters in the string.

Positive Lookahead (?=)

Positive lookahead asserts that the pattern inside the lookahead must match the text following the current position.

The syntax for positive lookahead is (?=...).

For example, the regex pattern go(?=ogle) matches go only if it is followed by ogle.

Negative Lookahead (?!)

Negative lookahead asserts that the pattern inside the lookahead must not match the text following the current position.

The syntax for negative lookahead is (?!...).

For example, the regex pattern go(?!ogle) matches go only if it is not followed by ogle.

Positive Lookbehind (?<=)

Positive lookbehind asserts that the pattern inside the lookbehind must match the text preceding the current position.

The syntax for positive lookbehind is (?<=...).

For example, the regex pattern (?<=go)gle matches gle only if it is preceded by go.

Negative Lookbehind (?<!)

Negative lookbehind asserts that the pattern inside the lookbehind must not match the text preceding the current position.

The syntax for negative lookbehind is (?<!...).

For example, the regex pattern (?<!go)gle matches gle only if it is not preceded by go.