Regular Expressions (Regex)

(Note to self: use Word to update the tables)

Metacharacters

Metacharacters are reserved characters, and they are:

{}[]()^$.|*+?-\

To find a metacharacter in a string, prefix it with a backslash, e.g. \. to find a dot, or \\ to find a backslash.

Find a character

a		a single character a
[abc]	(a|b|c)	any single character from the set, i.e. a, b, or c. For example, [bcr]at matches "bat", "cat", and "rat"
[^abc]		any single character except a, b, or c. For example, [^b]at matches "cat" and "rat", but not "bat"
[A-Z]		any character in the range A-Z, i.e. any uppercase letter
[a-z]		any character in the range a-z, i.e. any lowercase letter
[A-Za-z]		any character in the range A-Z or a-z, i.e. any letter
[0-9]	\d	any character in the range 0-9, i.e. any number
.		any single character
\.		a dot (prefix with a backslash as . is a metacharacter)
\\		a backslash character (prefix with a backslash as the backslash is a metacharacter itself)
\t		a tab character
\n		a new line character (also see $ is the end of line expression)
\s		any whitespace character, which includes space, tab and newline character
\w	[0-9a-zA-Z_]	any word character, which only includes any lowercase or uppercase letter, any number and the underscore character
\d		any digit
(a|b)		a or b

Line Characters

^	start of line
$	end of line
^$	empty string = ""

Quantification

a?	0 or 1 of a. For example, colou?r matches both "color" and "colour"
a*	0 or more of a. For example, ab*c matches "ac", "abc", "abbc", "abbbc", and so on
a+	1 or more of a. For example, ab+c matches "abc", "abbc", "abbbc", and so on, but not "ac"
a{3}	exactly 3 of a
a{3,}	3 or more of a
a{3,6}	between 3 and 6 of a

Grouping

(   )	capture group
\1	backreference to group #1

See also https://www.regular-expressions.info/index.html