Regular Expression Cheat Sheet

A specialised characteristic pattern which describes a certain amount of text is referred to as Regex or regexp (Regular expressions). When these patterns are used from any source it is called Regex Cheat sheet or regular expressions cheat sheet. In natural processing and various other tasks like common text data manipulation

More on regular expressions cheat sheet

There are several regex engines that can be used to process regexes. Regex engines act differently depending on the syntax they use, and you can get a list of most popular engines in this blog. Two of the common languages include Python and R, which have their own engines.

A regex or regular expression cheat sheet can be used to extract substrings from lower strings, check for patterns in a text, and modify text since it describes patterns of text. There are many different types of regex, including simple regex which describes specific words, and more complex regex which finds vague patterns of characters, such as the top-level domain at the end of a URL.

Definitions

Literal Character - You can use literal characters in regular expressions to represent actual characters. For example, if you want to represent an ”r”, then you would write “r”.
Metacharacter - A metacharacter is a character that tells the regex engine that the following character has a unique meaning(usually after /). Metacharacters can serve as markers for beginning, ending or matching single characters.
Character Class - In a character class(or character set ), the engine is instructed exactly what characters it should look for. It is denoted by [ and ], with the characters you wish to find between the brackets.
Capture Group - It allows you to group regexes together using round parenthesis (see below) and apply other regex features to the group such as quantifiers.

Regular expressions cheat sheets are a powerful tool for manipulating text and searching for patterns. Here's a cheat sheet of some of the most commonly used syntax and regex Python:

1. Anchors

These match a position just before or after any other character:

Syntax	Description	Example Pattern	Example Matches	Example non- matches
^, \A	Matches the start of line	^r, \Ar	run recess	dog cat
$, \Z	Match the end of line	n$, n\Z	corn fun	mobile speaker
\b	Match the characters at the start and end of a word	\brat\b	the rat ran the rat ate	ratskin ratflow
\B	Match characters in between of a word	\Boo \B	book shook	shoe flue

2. Matching types of character

The more specific type of character tp match is not just the character itself, but the type of character, such as letter, number, and more.

Syntax	Description	Example Pattern	Example Matches	Example non- matches
.	Anything except for a line break	c.e	cheap clean	Acert cent
\d	match a digit	\d	6060-896 2b\|^2b	Tw **___
\D	Match a non-digit	\D	The 5 cats ate 12 angry rats	52 10032
\w	Match word characters	\wee\w	Trees bees	The bee Eels eat skin
\W	Match non-word characters	\Wbat\W	At bat Swing the bat slow	Wombat bat53
\s	Match whitespace	\sfox\s	The fox ate The fox ran	It’s the fox fox-fur
\S	Match non-whitespace	\See\S	Trees beef	The bee stung The tall tree
\metacharacter	Escape a metacharacter to match on the metacharacter	\. \^	The cat ate. 2^3	The cat ate 23

3. Character classes

These are sets or ranges of characters

Syntax	Description	Example Pattern	Example Matches	Example non-matches
[xy]	Match several characters	gr[ea]y	Gray grey	Green greek
[x-y]	Match a range of characters	[a-e]	Amber brand	Fox join
[^xy]	Does not match several characters	gr[^ea]y	Green greek	Gray grey
[\ ^-]	Match metacharacters inside the character class	4[\^\.-+*/]\d	4^3 4.2	44 23

4. Repetition

The repeated appearance of characters can be matched rather than a single instance of them.

Syntax	Description	Example Pattern	Example Matches	Example non- matches
x*	Matches zero or more times	ar*o	Cacao carrot	Arugula artichoke
x+	Matches one or more times	re+	Green tree	Trap ruined
x?	Matches zero or one times	ro?a	roast rant	Root rear
x{m}	Match m times	\we{2}\w	deer seer	Red enter
x{m,}	Match m or more times	2{3,}4	671-2224 22224	224 123
x{m,n}	Match between m and n times	12{1,3}3	1234 1222389	15335 122223
*x?,x+?, etc**	match the minimum number of times - known as a lazy quantifier	re+?	Tree free	Trout roasted

5. Capturing, alternation & backreferences

Using the capture function, you can identify the parts of the string that you want to extract.

Syntax	Description	Example Pattern	Example Matches	Example non-matches
(x)	Capturing a pattern	(iss)+	Mississippi missed	Mist persist
(?:x)	Create a group without capturing	(?:ab)(cd)	Match: abcd Group 1: cd	acbd
(?<name>X)	Create a named capture group	(?<first>\d)(?<scrond>\d)\d*	Match: 1325 first: 1 second: 3	2 hello
(x\|y)	Match several alternative patterns	(re\|ba)	red banter	Rant bear
\n	reference previous captures where n is the group index starting at 1	(b)(\w*)\1	blob bribe	Bear bring
\k<name>	Reference named captures	(?<first>5)(\d*)\k<first>	51245 55	523 51

6. Lookahead

Characters can be specified before or after matching, without those characters appearing in the match.

Syntax	Description	Example Pattern	Example Matches	Example non-matches
(?=x)	looks ahead at the next characters without using them in the match	an(?=an) iss(?=ipp)	banana Mississippi	band missed
(?!x)	looks ahead at next characters to not match on	ai(?!n)	fail brail	faint train
(?<=x)	looks at previous characters for a match without using those in the match	(?<=tr)a	trail translate	bear streak
(?<!x)	looks at previous characters to not match on	(?!tr)a	bear translate	trail strained

7. Literal matches and modifiers

Changing the matching rules using modifiers changes how they work.

Syntax	Description	Example Pattern	Example Matches	Example non- mathes
\Qx\E	match start to finish	\Qtell\E \Q\d\E	tell \d	I’ll tell you this I have 5 coins
(?i)x(?-i)	set the regex string to case-insensitive	(?i)te(?-i)	sTep tEach	Trench bear
(?x)x(?-x)	regex ignores whitespace	(?x)t a p(?-x)	tap tapdance	c a t rot a potato
(?s)x(?-s)	turns on single-line/DOTALL mode which makes the “.” include new-line symbols (\n) in addition to everything else	(?s)first and second(?-s) and third	first and Second and third	first and second and third
(?m)x(?-m)	Changes ^ and $ to be end of line rather than end of string	^eat and sleep$	eat and sleep eat and sleep	treat and sleep eat and sleep.

8. Unicode

Chinese characters and emojis can be used with regular expressions beyond the Roman alphabet.

Code points - In a system such as Unicode, an abstract character is represented by a hexadecimal number.
Graphemes - The alphabet consists of a series of graphemes, which are either code points or characters.

Syntax

Description

Example Pattern

Example Matches

Example non-matches

match graphemes

\u0000gmail

@gmail www.email@gmail

gmail

@aol

\X\X

Match special characters like ones with an accent

\u00e8 or \u0065\u0300

Regular expressions cheat sheets can be complex and powerful, but also difficult to master. This regex cheat sheet covers some of the most commonly used patterns and syntax, but there are many more possibilities and combinations.

In conclusion, a regex cheatsheet is a quick reference guide that provides a comprehensive list of regular expressions and their corresponding meanings. It is a helpful tool for developers, data analysts, and anyone who works with text data and needs to extract, search or replace specific patterns.

A regex cheat sheet typically includes a variety of regular expression syntaxes, such as anchors, quantifiers, character classes, groups, and assertions. It also covers special characters and metacharacters that have specific meanings within regular expressions, such as the dot (.), caret (^), dollar sign ($), and backslash ().

Using a regex cheatsheet can save time and increase productivity by allowing users to quickly and easily identify the appropriate regular expression pattern for a particular task. However, it is important to keep in mind that regular expressions can be complex and may require additional practice and experimentation to master.’

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