Types of regular expressions

Anchors

^	Start of string, or start of line in multi-line pattern
\A	Start of string
$	End of string, or end of line in multi-line pattern
\Z	End of string
\b	Word boundary
\B	Not word boundary
\<	Start of word
\>	End of word

[abc]	A single character of: a, b or c
[^abc]	A character except: a, b or c. The caret ^ negates character classes
[a-z]	A character in the range: a-z
[^a-z]	A character not in the range: a-z
[0-9]	A digit in the range: 0-9
[a-zA-Z]	A character in the range:a-z or A-Z
[a-zA-Z0-9]	A character in the range:a-z, A-Z or 0-9

Class	Same as	Description
[[:alnum:]]	[0-9A-Za-z]	Matches any alphanumeric character 0–9, A–Z, or a–z
[[:alpha:]]	[A-Za-z]	Matches any alphabetical character, either upper or lower case
[[:blank:]]	[\t ]	Matches a space or Tab character
[[:digit:]]	[0-9]	Matches a numerical digit from 0 through 9
[[:graph:]]	[[:alnum:][:punct:]]	Visible characters (not space)
[[:lower:]]	[a-z]	Matches any lowercase alphabetical character a–z
[[:print:]]	[ -~] == [ [:graph:]]	Matches any printable character
[[:punct:]]	[!"#$%&’()*+,-./:;<=>?@[]^_`{	}~]
[[:space:]]	[\t\n\v\f\r ]	Matches any whitespace character: space, Tab, NL(newline), FF (formfeed), VT (vertical tab), CR (carriage return)
[[:upper:]]	[A-Z]	Matches any uppercase alphabetical character A–Z
[[:word:]]	[0-9A-Za-z_]	Matches all world characters
[[:xdigit:]]	[0-9A-Fa-f]	Matches all hexadecimal digits
[[:<:]]	[\b(?=\w)]	Matches start of word
[[:>:]]	[\b(?<=\w)]	Matches end of word
[[:ascii:]]	[\x00-\x7F]	ASCII codes 0-127
[[:cntrl:]]	[\x00-\x1F\x7F]	Control characters

?	Match an Element Zero or One Time
*	Match an Element Zero or More Times
+	Match an Element One or More Times
[0-9]+	Any digit from 0-9 must appear 1 or more times.
{}	Match an Element a Specific Number of Times
a{m}	The character a must appear exactly m times.
a{m,n}	The character a must appear at least m times, but no more than n times.
a{m,}	The character a must appear m or more times.
a*	Greedy quantifier
a*?	Lazy quantifier
a*+	Possessive quantifier
{,n}	Match the preceding element if it occurs no more than m times.

<aside> 💡 Common Meta-characters ^ ( { | * < $ ) ? > . + [ \\
Escape these special characters with \\

</aside>

.	Any character except new line (\n)
(a	b)
(...)	Group
(?:...)	Passive (non-capturing) group
[abc]	Range (a or b or c)
[^abc]	Not (a or b or c)
[a-q]	Lower case letter from a to q
[A-Q]	Upper case letter from A to Q
[0-7]	Digit from 0 to 7
\x	Group/subpattern number "x"

g	Global match
i *	Case-insensitive
m *	Multiple lines
s *	Treat string as single line
x *	Allow comments and whitespace in pattern
e *	Evaluate replacement
U *	Ungreedy pattern

\	Escape following character
\Q	Begin literal sequence
\E	End literal sequence

<aside> 💡 What is Escaping?

Escaping is a method of treating characters with special meanings in regular expressions literally rather than as special characters.

</aside>