Regular expression syntax cheatsheet This page provides an overall cheat sheet of all the capabilities of RegExp syntax by aggregating the content of the articles in the RegExp guide. If you need more information on a specific topic, please follow the link on the corresponding heading to access the full article or head to the guide. As part of resources, you will get this high-quality cheat-sheet for regex language. And the supported operations. Besides, we will use an interactive regex tool to write and test patterns. In the JavaScript Regex features section, you will get familiar with various regex methods, their purpose, and how to unit test your pattern.

Above diagram created using Regulex

Cheatography Cheat Sheet. This JavaScript Cheat sheet is formulated by Dave Child. It enlists all the. Test your regex by visualizing it with a live editor. JavaScript, Python, and PCRE.

This blog post gives an overview of regular expression syntax and features supported by JavaScript. Examples have been tested on Chrome/Chromium console (version 81+) and includes features not available in other browsers and platforms. Assume ASCII character set unless otherwise specified. This post is an excerpt from my JavaScript RegExp book.

Elements that define a regular expression🔗

Note	Description
MDN: Regular Expressions	MDN documentation for JavaScript regular expressions
/pat/	a RegExp object
const pet = /dog/	save regexp in a variable for reuse, clarity, etc
/pat/.test(s)	Check if given pattern is present anywhere in input string
returns true or false
i	flag to ignore case when matching alphabets
g	flag to match all occurrences
new RegExp('pat', 'i')	construct RegExp from a string
second argument specifies flags
use backtick strings with ${} for interpolation
source	property to convert RegExp object to string
helps to insert a RegExp inside another RegExp
flags	property to get flags of a RegExp object
s.replace(/pat/, 'repl')	method for search and replace
s.search(/pat/)	gives starting location of the match or -1
s.split(/pat/)	split a string based on regexp

Anchors	Description
^	restricts the match to start of string
$	restricts the match to end of string
m	flag to match the start/end of line with ^ and $ anchors
r, n, u2028 and u2029 are line separators
dos-style files use rn, may need special attention
b	restricts the match to start/end of words
word characters: alphabets, digits, underscore
B	matches wherever b doesn't match

Epson l800 for mac driver. ^, $ and are metacharacters in the above table, as these characters have special meaning. Prefix a character to remove the special meaning and match such characters literally. For example, ^ will match a ^ character instead of acting as an anchor.

Feature	Description
pat1|pat2|pat3	multiple regexp combined as OR conditional
each alternative can have independent anchors
(pat)	group pattern(s), also a capturing group
a(b|c)d	same as abd|acd
(?:pat)	non-capturing group
(?<name>pat)	named capture group
.	match any character except line separators
[]	Character class, matches one character among many

Greedy Quantifiers	Description
?	match 0 or 1 times
*	match 0 or more times
+	match 1 or more times
{m,n}	match m to n times
{m,}	match at least m times
{n}	match exactly n times
pat1.*pat2	any number of characters between pat1 and pat2
pat1.*pat2|pat2.*pat1	match both pat1 and pat2 in any order

Greedy here means that the above quantifiers will match as much as possible that'll also honor the overall regexp. Hp laserjet m1132 driver for mac. Appending a ? to greedy quantifiers makes them non-greedy, i.e. match as minimally as possible. Quantifiers can be applied to literal characters, groups, backreferences and character classes.

Character class	Description
[ae;o]	match any of these characters once
[3-7]	range of characters from 3 to 7
[^=b2]	negated set, match other than = or b or 2
[a-z-]	- should be first/last or escaped using to match literally
[+^]	^ shouldn't be first character or escaped using
[]]	] and should be escaped using
w	similar to [A-Za-z0-9_] for matching word characters
d	similar to [0-9] for matching digit characters
s	similar to [ tnrfv] for matching whitespace characters
use W, D, and S for their opposites respectively
u	flag to enable unicode matching
p{}	Unicode character sets
P{}	negated unicode character sets
see MDN: Unicode property escapes for details
u{}	specify unicode characters using codepoints

Lookarounds	Description
lookarounds	allows to create custom positive/negative assertions
zero-width like anchors and not part of matching portions
(?!pat)	negative lookahead assertion
(?<!pat)	negative lookbehind assertion
(?=pat)	positive lookahead assertion
(?<=pat)	positive lookbehind assertion
variable length lookbehind is allowed
(?!pat1)(?=pat2)	multiple assertions can be specified next to each other in any order
as they mark a matching location without consuming characters
((?!pat).)*	Negates a regexp pattern

Matched portion	Description
m = s.match(/pat/)	assuming g flag isn't used and regexp succeeds,
returns an array with matched portion and 3 properties
index property gives the starting location of the match
input property gives the input string s
groups property gives dictionary of named capture groups
m[0]	for above case, gives entire matched portion
m[N]	matched portion of Nth capture group
s.match(/pat/g)	returns only the matched portions, no properties
s.matchAll(/pat/g)	returns an iterator containing details for
each matched portion and its properties
Backreference	gives matched portion of Nth capture group
use $1, $2, $3, etc in replacement section
$& gives entire matched portion
$` gives string before the matched portion
$' gives string after the matched portion
use 1, 2, 3, etc within regexp definition
$$	insert $ literally in replacement section
$0N	same as $N, allows to separate backreference and other digits
Nxhh	allows to separate backreference and digits in regexp definition
(?<name>pat)	named capture group
use k<name> for backreferencing in regexp definition
use $<name> for backreferencing in replacement section

Regular expression examples🔗

Regex Builder

• test method

• new RegExp() constructor

• string and line anchors

• replace method and word boundaries

• alternations and grouping

• MDN: Regular Expressions doc provides escapeRegExp function, useful to automatically escape metacharacters.
  • See also XRegExp utility which provides XRegExp.escape and XRegExp.union methods. The union method has additional functionality of allowing a mix of string and RegExp literals and also takes care of renumbering backreferences.

• dot metacharacter and quantifiers

Javascript Regex Cheat Sheet 2019

• match method

• matchAll method

• function/dictionary in replacement section

• split method

• backreferencing with normal/non-capturing/named capture groups

Node Js Regex Cheat Sheet

• examples for lookarounds

Debugging and Visualization tools🔗

As your regexp gets complicated, it can get difficult to debug if you run into issues. Building your regexp step by step from scratch and testing against input strings will go a long way in correcting the problem. To aid in such a process, you could use various online regexp tools.

regex101 is a popular site to test your regexp. You'll have first choose the flavor as JavaScript. Then you can add your regexp, input strings, choose flags and an optional replacement string. Matching portions will be highlighted and explanation is offered in separate panes. There's also a quick reference and other features like sharing, code generator, quiz, etc.

Another useful tool is jex: regulex which converts your regexp to a rail road diagram, thus providing a visual aid to understanding the pattern.

JavaScript RegExp book🔗

Javascript Regex Cheat Sheet Excel

Visit my repo learn_js_regexp for details about the book I wrote on JavaScript regular expressions. Machine id for mac. The ebook uses plenty of examples to explain the concepts from the basics and includes exercises to test your understanding. The cheatsheet and examples presented in this post are based on contents of this book.