Regular Expressions Syntax

Syntax	Description
?	Match the preceding character or subexpression 0 or 1 times. Also used for non-capturing groups, and named capturing groups.
*	Match the preceding character or subexpression 0 or more times.
+	Match the preceding character or subexpression 1 or more times.
{n}	Match the preceding character or subexpression exactly n times.
{min,}	Match the preceding character or subexpression min or more times.
{,max}	Match the preceding character or subexpression max or fewer times.
{min,max}	Match the preceding character or subexpression at least min times but no more than max times.
-	when included between square brackets indicates to; e.g. [3-6] matches characters 3, 4, 5, or 6.
^	start of string (or start of line if the multiline /m option is specified), or negates a list of options (i.e. if within square brackets [])
$	end of string (or end of line if the multiline /m option is specified).
(...)	groups subexpressions, captures matching content in special variables (\1, \2, etc.) that can be used later within the same regex, for example (\w+)\s\1\s matches word repetition
(?:...)	groups subexpressions without capturing
.	matches any character except line-feed (\n).
[...]	any character between these brackets should be matched once. NB: ^ following the open bracket negates this effect. - occurring inside the brackets allows a range of values to be specified (unless it's the first or last character, in which case it just represents a regular dash).
\	escapes the following character. Also used in meta sequences - regex tokens with special meaning.
\$	dollar (i.e. an escaped special character)
\(	open parenthesis (i.e. an escaped special character)
\)	close parenthesis (i.e. an escaped special character)
\*	asterisk (i.e. an escaped special character)
\.	dot (i.e. an escaped special character)
\?	question mark (i.e. an escaped special character)
\[	left (open) square bracket (i.e. an escaped special character)
\\	backslash (i.e. an escaped special character)
\]	right (close) square bracket (i.e. an escaped special character)
\^	caret (i.e. an escaped special character)
\{	left (open) curly bracket / brace (i.e. an escaped special character)
\|	pipe (i.e. an escaped special character)
\}	right (close) curly bracket / brace (i.e. an escaped special character)
\+	plus (i.e. an escaped special character)
\a	alarm
\b	word (alphanumeric sequence) boundary
\1,\2, etc.	back-references to previously matched subexpressions, grouped by (), \1 means first match, \2 means second match etc.
[\b]	backspace - when \b is inside a character class ( [] )matches backspace
\B	negated \b - matches at any position between two word characters as well as at any position between two non-word characters
\D	non-digit
\d	digit
\e	escape
\f	form feed
\n	line feed
\r	carriage return
\S	non-white-space
\s	white-space
\t	tab
\v	vertical tab
\W	non-word
\w	word (i.e. alphanumeric character)
{...}	named character set
|	or; i.e. delineates the prior and preceding options.