![]() The engine does not advance to the next character in the string, because the previous regex token was zero-length. The engine continues with the next token: the literal i. \b matches here, because the T is a word character and the character before it is the void before the start of the string. Since this token is zero-length, the position before the character is inspected. The engine starts with the first token \b at the first character T. Let’s see what happens when we apply the regex \b is \b to the string This island is beautiful. Effectively, \B matches at any position between two word characters as well as at any position between two non-word characters. \B matches at every position where \b does not. So saying “ \b matches before and after an alphanumeric sequence” is more exact than saying “before and after a word”. This regex does not match 44 sheets of a4. Since digits are considered to be word characters, \b 4 \b can be used to match a 4 that is not part of a larger number. Using only one operator makes things easier for you. This is because any position between characters can never be both at the start and at the end of a word. ![]() Most flavors, except the ones discussed below, have only one metacharacter that matches both before a word and after a word. Java supports Unicode for \b but not for \w. In most flavors, characters that are matched by the short-hand character class \w are the characters that are treated as word characters by word boundaries. All characters that are not “word characters” are “non-word characters”.Įxactly which characters are word characters depends on the regex flavor you’re working with. A “word character” is a character that can be used to form words. ![]() Simply put: \b allows you to perform a “whole words only” search using a regular expression in the form of \b word \b. Between two characters in the string, where one is a word character and the other is not a word character.After the last character in the string, if the last character is a word character.Before the first character in the string, if the first character is a word character.There are three different positions that qualify as word boundaries: It matches at a position that is called a “word boundary”. The metacharacter \b is an anchor like the caret and the dollar sign. ![]()
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