Some basic regex rules

regex-fiddle

Good tester: http://www.regexr.com/
Cheat sheet: http://ole.michelsen.dk/tools/regex.html

| = or
(ab|ba)
() = capture
(Java|Ecma)Script
(?:Java|Ecma)Script => don't care about capture

// negated character classes
[^g-z]
// shortcuts
\W = [^\w]
\D = [^\d]
\S = [^\s]

/#\w{3,6}/g = hex
#123ABC
#abc

hello6jkhkjhkjh987
2020-01-32

Ranges
[\w-] = word characters + hyphens
\s = whitespace =~[\t\r\n]
\d = [0-9] (not decimals)

// no look behind in javascipt (does not effect match position
// look ahead - when not followed by
a(?!b)
ab ac
// look ahead
(what is want a that is followed by a b, but do not match the b)
look aheads can contain capture groups
a(?=b)
ab

\B - non-word boundary = between \w and \w or \W and \W
\b = boundary (useful for checking if string is in list) (between \w and \W)
/^ = beginning of line
$/ = end of line
/^hello$/ = match only hello on a line (use /m for multi line)

hello
[-+]?\d*(?:\.\d+)?
15
134.2020
-.2000
.293
20


\w = [a-zA-Z0-9_]
[a-z]
[a-z0-9_]
// most characters do not need escaping in range

Sets
[abc]
[abc]+ // 1 or more of any of thses

// regex = greey -> '?' turns off greedyness
a{0,1} a? => 0 to 1
a{1,} a+ => 1 to many
a{0,} a* => 0 to many
aaaaaaaaaaaa (a{12})
{} = quatifier