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Regular Expression Reference: Word Boundaries

Feature	Syntax	Description	Example	JGsoft	.NET	Java	Perl	PCRE	PCRE2	PHP	Delphi	R	JavaScript	VBScript	XRegExp	Python	Ruby	std::regex	Boost	Tcl ARE	POSIX BRE	POSIX ERE	GNU BRE	GNU ERE	Oracle	XML	XPath
Word boundary	`\b`	Matches at a position that is followed by a word character but not preceded by a word character, or that is preceded by a word character but not followed by a word character.	`\b.` matches `a`, , and `d` in `abc def`	Unicode	non‑ECMA Unicode	ASCII	Unicode	ASCII	ASCII	5.3.4 Unicode 5.0.0 code page	ASCII	ASCII	ASCII	ASCII	ASCII	3.0 Unicode 2.4 ASCII	Unicode	ECMA ASCII	ECMA extended egrep awk Unicode	no	no	no	ASCII	ASCII	no	no	no
Word boundary	`\B`	Matches at a position that is preceded and followed by a word character, or that is not preceded and not followed by a word character.	`\B.` matches `b`, `c`, `e`, and `f` in `abc def`	Unicode	non‑ECMA Unicode	ASCII	Unicode	ASCII	ASCII	5.3.4 Unicode 5.0.0 code page	ASCII	ASCII	ASCII	ASCII	ASCII	3.0 Unicode 2.4 ASCII	Unicode	ECMA ASCII	ECMA extended egrep awk Unicode	no	no	no	ASCII	ASCII	no	no	no
Tcl word boundary	`\y`	Matches at a position that is followed by a word character but not preceded by a word character, or that is preceded by a word character but not followed by a word character.	`\y.` matches `a`, , and `d` in `abc def`	Unicode	no	no	no	no	no	no	no	no	no	no	no	no	no	no	no	Unicode	no	no	no	no	no	no	no
Tcl word boundary	`\Y`	Matches at a position that is preceded and followed by a word character, or that is not preceded and not followed by a word character.	`\Y.` matches `b`, `c`, `e`, and `f` in `abc def`	Unicode	no	no	no	no	no	no	no	no	no	no	no	no	no	no	no	Unicode	no	no	no	no	no	no	no
Tcl word boundary	`\m`	Matches at a position that is followed by a word character but not preceded by a word character.	`\m.` matches `a` and `d` in `abc def`	Unicode	no	no	no	no	no	no	no	no	no	no	no	no	no	no	no	Unicode	no	no	no	no	no	no	no
Tcl word boundary	`\M`	Matches at a position that is preceded by a word character but not followed by a word character.	`.\M` matches `c` and `f` in `abc def`	Unicode	no	no	no	no	no	no	no	no	no	no	no	no	no	no	no	Unicode	no	no	no	no	no	no	no
GNU word boundary	`\<`	Matches at a position that is followed by a word character but not preceded by a word character.	`\<.` matches `a` and `d` in `abc def`	no	no	no	no	no	no	no	no	no	no	no	no	no	no	no	ECMA extended egrep awk Unicode	no	no	no	ASCII	ASCII	no	no	no
GNU word boundary	`\>`	Matches at a position that is preceded by a word character but not followed by a word character.	`.\>` matches `c` and `f` in `abc def`	no	no	no	no	no	no	no	no	no	no	no	no	no	no	no	ECMA extended egrep awk Unicode	no	no	no	ASCII	ASCII	no	no	no
POSIX word boundary	`[[:<:]]`	Matches at a position that is followed by a word character but not preceded by a word character.	`[[:<:]].` matches `a` and `d` in `abc def`	no	no	no	no	8.34 ASCII	ASCII	5.5.10 Unicode	XE7 ASCII	3.0.3 ASCII	no	no	no	no	no	no	Unicode	Unicode	ASCII	ASCII	no	no	no	no	no
POSIX word boundary	`[[:>:]]`	Matches at a position that is preceded by a word character but not followed by a word character.	`.[[:>:]]` matches `c` and `f` in `abc def`	no	no	no	no	8.34 ASCII	ASCII	5.5.10 Unicode	XE7 ASCII	3.0.3 ASCII	no	no	no	no	no	no	Unicode	Unicode	ASCII	ASCII	no	no	no	no	no
Word boundary behavior		Word boundaries always match at the start of the match attempt if that position is followed by a word character, regardless of the character that precedes the start of the match attempt. (Thus word boundaries are not handled correctly for the second and following match attempts in the same string.)	`\b.` matches all of the letters but not the space when iterating over all matches in the string `abc def`	no	no	no	no	no	no	no	no	no	no	no	no	no	no	no	no	YES	no	no	YES	YES	no	no	no
Feature	Syntax	Description	Example	JGsoft	.NET	Java	Perl	PCRE	PCRE2	PHP	Delphi	R	JavaScript	VBScript	XRegExp	Python	Ruby	std::regex	Boost	Tcl ARE	POSIX BRE	POSIX ERE	GNU BRE	GNU ERE	Oracle	XML	XPath