Basics

Look around basics

Lookarounds often cause confusion to new regex learners. There are four lookarounds:

(?<= … ) and (?= … ),

(?<! … ) and (?! … )

Collectively, lookbehinds and lookaheads are known as lookarounds. Let’s see the following table of examples:

Lookaround Name What it Does
(?=learn) Lookahead Asserts that what immediately follows the current position in the string is learn
(?<=learn) Lookbehind Asserts that what immediately precedes the current position in the string is learn
(?!learn) Negative Lookahead Asserts that what immediately follows the current position in the string is not learn
(?<!learn) Negative Lookbehind Asserts that what immediately precedes the current position in the string is not learn

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