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Regular Expression Reference: Word Boundaries

Feature	Syntax	Description	Example	JGsoft	Python	JavaScript	VBScript	XRegExp	.NET	Java	ICU	RE2	Perl	PCRE	PCRE2	PHP	Delphi	R	Ruby	std::regex	Boost	Tcl	POSIX	GNU	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	3.0 Unicode 2.4 ASCII	ASCII	ASCII	ASCII	non‑ECMA Unicode	ASCII	Unicode	default ASCII	Unicode	ASCII	ASCII	Unicode	ASCII	ASCII	1.9 Unicode 1.8 ASCII	ECMA ASCII	ECMA extended egrep awk Unicode	no	no	ASCII	no	no	no
Word non-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	3.0 Unicode 2.4 ASCII	ASCII	ASCII	ASCII	non‑ECMA Unicode	ASCII	Unicode	default ASCII	Unicode	ASCII	ASCII	Unicode	ASCII	ASCII	1.9 Unicode 1.8 ASCII	ECMA ASCII	ECMA extended egrep awk Unicode	no	no	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	no	no	Unicode	no	no	no	no	no
Tcl word non-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	no	no	Unicode	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	no	no	Unicode	no	no	no	no	no
Tcl end-of-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	no	no	Unicode	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	no	no	ECMA extended egrep awk Unicode	no	no	ASCII	no	no	no
GNU end-of-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	no	no	ECMA extended egrep awk Unicode	no	no	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	no	no	no	no	no	no	8.34 ASCII	ASCII	5.5.10 Unicode	XE7 ASCII	3.0.3 ASCII	no	no	Unicode	Unicode	ASCII	no	no	no	no
POSIX end-of-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	8.34 ASCII	ASCII	5.5.10 Unicode	XE7 ASCII	3.0.3 ASCII	no	no	Unicode	Unicode	ASCII	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	no	no	YES	no	YES	no	no	no
UAX 29 word boundary	`\b` and `\B`	Matches at a word boundary ÷ and \B matches at a word non-boundary × according to Unicode Standard Annex #29.	`(?w)\b.\b` matches `!` because the WB1 and WB2 rules in UAX 29 treat the start and end of the string as a word boundary.	no	no	no	no	no	no	no	option	no	no	no	no	no	no	no	no	no	no	n/a	n/a	no	n/a	n/a	n/a
UAX 29 word boundary	`\b{wb}`	Matches at a word boundary ÷ according to Unicode Standard Annex #29.	`\b{wb}.\b{wb}` matches `!` because the WB1 and WB2 rules in UAX 29 treat the start and end of the string as a word boundary.	no	no	no	no	no	no	no	no	no	5.22	no	no	no	no	no	no	no	no	no	no	no	no	no	no
UAX 29 word non-boundary	`\b{wb}`	Matches at a word non-boundary × according to Unicode Standard Annex #29.	`\B{wb}'\B{wb}` matches `'` in `John's` because the WB6 and WB7 rules in UAX 29 treat the positions before and after a hyphen between two letters as a word non-boundary.	no	no	no	no	no	no	no	no	no	5.22	no	no	no	no	no	no	no	no	no	no	no	no	no	no
Feature	Syntax	Description	Example	JGsoft	Python	JavaScript	VBScript	XRegExp	.NET	Java	ICU	RE2	Perl	PCRE	PCRE2	PHP	Delphi	R	Ruby	std::regex	Boost	Tcl	POSIX	GNU	Oracle	XML	XPath

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