Shorthands for character classes and anchors

Regex	What it Matches	Inversion
\d	[0-9] or with Unicode all digits. Not in AWK.	\D
\w	[A-Za-z0-9_] or with Unicode all word characters	\W
\s	[ \t\r\n\f] or all whitespace	\S
\b, AWK and Tcl:\y	Matches the boundary at the start or end of a word. Is \y in AWK and Tcl as there \b means backspace.	\B, Tcl: \Y

Some specialties

All of these specialties do not work in AWK nor in GAWK. They do work in Perl, probably.

Regex	Name	What it Does
(?:bar)	non-capturing	Matches bar, but doesn’t capture it.
(?=foo)	lookahead	Asserts that what immediately follows the current position in the string is foo.
(?<=bar)	lookbehind	Asserts that what immediately precedes the current position in the string is bar.
(?!baz)	negative lookahead	Asserts that what immediately follows the current position in the string is not baz.
(?<!foo)	negative lookbehind	Asserts that what immediately precedes the current position in the string is not foo.
(?i)	case-insensitive	Turns on case-insensitive matching. Not in AWK. AWK has no really short way to match case-insensitive. One can use `BEGIN{IGNORECASE=1}` as starting block or `tolower($0)~/abc/` instead of `/abc/`
(?m)	multi-line	Turns on multi-line mode. $ and ^ match at any line, not only at begin and start of text. Not in AWK.
(?x)	comment	Activates comment-mode. Whitespace is ignored and a # in a line starts a comment. Not in AWK.
\b AWK:\y	word boundary	Matches the boundary at the start or end of a word. \y in AWK as there \b means backspace.
(?<g>xi)	named group	Matches xi and gives the capture group the name g. Access to group in code: `m.groups["g"]`. Only in .NET like this. Some other systems have other possibilities for named groups.