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>