Understand Regular Expression

Character	Description
\w	Matches any word character (alphanumeric).
\W	Matches any non-word character.
\s	Matches any whitespace character (tab, newline, carriage return, form feed, vertical tab).
\S	Matches any non-whitespace character.
\d	Matches any numerical digit.
\D	Matches any character that is not a number.
[\b]	Matches a backspace.
.	Matches any character except a newline.
[...]	Matches any one character within the brackets.
[^...]	Matches any one character not within the brackets.
[x-y]	Matches any character in the range of x to y.
[^x-y]	Matches any character not in the range of x to y.
{x,y}	Matches the previous item at least x times but not to exceed y times.
{x,}	Matches the previous item at least x times.
{x}	Matches the previous item exactly x times.
?	Matches the previous item once or not at all.
+	Matches the previous item at least once.
*	Matches the previous item any number of times or not at all.
|	Matches the expression to the left or the right of the | character.
(...)	Group everything inside parentheses into a subpattern.
\x	Matches the same characters that resulted from the subpattern in group number x. Groups, which are designated with parentheses, are numbered from left to right.
^	Matches the beginning of the string or beginning of a line, in multiline matches.
$	Matches the end of the string or end of a line, in multiline matches.
\b	Matches the position between a word character and a non-word character.
\B	Matches the position that is not between a word character and a non-word character.

Know More in Regular Expression
Character	Description
\f	Form feed
\n	Newline
\r	Carriage return
\t	Tab
\v	Vertical tab
\/	Forward slash (/)
\\	Backward slash (\)
\.	Period (.)
\*	Asterisk (*)
\+	Plus (+)
\?	Question Mark (?)
\|	Horizontal bar (|)
\(	Left parenthesis (
\)	Right parenthesis )
\[	Left bracket ([)
\]	Right bracket (])
\{	Left curly brace ({)
\}	Right curly brace (})
\XXX	ASCII character represented by the octal number XXX
\xHH	ASCII character represented by the hexadecimal number HH
\cX	The control character represented by X