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Regex

Regular expressions are special characters which help search data, matching complex patterns.

Basic regex

Symbol	Descriptions
.	replaces any character
^	matches start of string
$	matches end of string
*	matches up zero or more times the preceding character
\	Represent special characters
()	Groups regular expressions
?	Matches up exactly one character

Character	Legend	Example	Sample Match
\d	Most engines: one digit from 0 to 9	file_\d\d	file_25
\d	.NET, Python 3: one Unicode digit in any script	file_\d\d	file_9੩
\w	Most engines: “word character”: ASCII letter, digit or underscore	\w-\w\w\w	A-b_1
\w	.Python 3: “word character”: Unicode letter, ideogram, digit, or underscore	\w-\w\w\w	字-ま_۳
\w	.NET: “word character”: Unicode letter, ideogram, digit, or connector	\w-\w\w\w	字-ま‿۳
\s	Most engines: “whitespace character”: space, tab, newline, carriage return, vertical tab	a\sb\sc	a b c
\s	.NET, Python 3, JavaScript: “whitespace character”: any Unicode separator	a\sb\sc	a b c
\D	One character that is not a digit as defined by your engine's \d	\D\D\D	ABC
\W	One character that is not a word character as defined by your engine's \w	\W\W\W\W\W	*-+
\S	One character that is not a whitespace character as defined by your engine's \s	\S\S\S\S	Yoyo

Quantifier	Legend	Example	Sample Match
+	One or more	Version \w-\w+	Version A-b1_1
{3}	Exactly three times	\D{3}	ABC
{2,4}	Two to four times	\d{2,4}	156
{3,}	Three or more times	\w{3,}	regex_tutorial
*	Zero or more times	ABC*	AAACC
?	Once or none	plurals?	plural

These expressions tell us about the number of occurrences of a character in a string.

Expression	Description
{n}	Matches the preceding character appearing 'n' times exactly
{n,m}	Matches the preceding character appearing 'n' times but not more than m
{n, }	Matches the preceding character only when it appears 'n' times or more

These regular expressions contain combinations of more than one expression.

Expression	Description
\+	Matches one or more occurrence of the previous character
\?	Matches zero or one occurrence of the previous character

The syntax for brace expansion is either a sequence or a comma separated list of items inside curly braces “{}”.

The starting and ending items in a sequence are separated by two periods “..”.

Expression	Description
{a,b,c,d}	Matches the actual characters in the braces. Example: echo {a,b,c,d}
{a..z}	Matches a thru z. Example: echo {a..z}
{0..9}	Matches 0 thru 9. Example: echo {0..9}