A .NET online regex tester: http://regexstorm.net/tester
RexEgg is a site containing black belt stuff concerning regexes and also a regex cheat sheet.
Another site containing fine info about Regexes.
One more, called Regextutorial.
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|
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
|(?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: