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Regex Cheat Sheet

Emma Bostian ✨ on February 19, 2019

A regular expression, or 'regex', is used to match parts of a string. Below is my cheat sheet for creating regular expressions. Testing a regex...

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Brian Kichler • Feb 19 '19

I go cross-eyed dealing with regex, but this is an excellent reference I'm definitely coming back to. I almost always head to regex101.com whenever pattern-matching starts to devour my brain.

Richard vK • Feb 20 '19

Just shared the link to regex101 with my colleagues today - great tool!

Burlacu Vasilii • Nov 8 '19

Yep, regex101 helps a lot! It even gives you the code snippet for your programming language (e.g. PHP)

Saúl Blanco Tejero • Feb 20 '19

Alex Lohr • Feb 19 '19

Using the | operator is a dangerous habit. You easily forget to guard yourself against matching substrings, for example consider the following line:

const isLocalHost = /127.0.0.1|localhost/.test(location.host);

And now what happens on localhost.mydevious.url? The secure solution is to use ^ and $ to gate the start and end of the tested string.

Also, one trick up JS regex's sleeve is the back reference (\1-\9):

/(["'])(.*?)\1/.test('"I can match Emma\'s full strings"') && RegExp.$2;
/(["'])(.*?)\1/.test("'I can match when Emma say \"things in strings\"'") && RegExp.$2;

This will re-use the (matches) inside the same regex.

Chris Watson • Feb 25 '19

The real guard is to write tests to assert the correct behaviour :)

Alex Lohr • Feb 26 '19

Just don't forget about those edge cases ;-)

Nick Taylor • Feb 19 '19

Todd Motto™

@toddmotto

Just remember, Elon Musk doesn’t know RegExp either.

19:45 PM - 19 Feb 2019

29 175

Sebastijan Grabar • Feb 21 '19

The funny thing about these Regex cheat cheets is no matter how many of them I put in my bookmarks, I never end up using them.

Colin O'Dell • Feb 5 '21

That's why you need a regex cheat sheet mug!

Precious adeyinka • Feb 26 '19

sebastian 😂 me too

Miloslav 🏳️‍🌈 🦋 Voloskov • Feb 19 '19 • Edited

For me, Regex and Perl are write-only languages. I can't debug, edit or even read regex – I just rewrite it from scratch with some tool like RegExr or something. For me, a person who can memorise all that syntax is definitely a superhuman.

Denys Séguret • Feb 19 '19 • Edited

Making code readable is half the job of the coder. It's also true for regexes, which means you have to look for ways to separate parts and comment your regexes (or at least name the groups).

Fortunately, you can find solutions in most languages. Here are two examples from some of my OS codes:

In Javascript:

    cmdArgRegex = miaou.lib("rex")`
            ([a-z ]*)                        // options (optional)
            (-?\d*\s*d\s*[\d+-]+)            // left rolldef (mandatory)
            (?:                              // inequation (optional)
                    \s*
                    ([<>=]+)                 // operator
                    \s*
                    ([\w+-]+)                // right rolldef or scalar
            )?
            \s*$
            /i`;

(I think there are JS libs to do that without taking my code, now)

In rust:

        static ref RE: Regex = Regex::new(
            r"(?x)
            ^
            (?P<slash_before>/)?
            (?P<pattern>[^\s/:]+)?
            (?:/(?P<regex_flags>\w*))?
            (?:[\s:]+(?P<verb>\S*))?
            $
            "

(this is the standard way in this language)

George WL • Feb 19 '19

I tend to not bother learning regex, the cases where it's useful, I'll just go to a site like regexr.com and then use their tools to build one.

Jackson Elfers • Feb 20 '19

In think that's the general consensus. I only use it occasionally so it's not worth my time to be 100 percent fluent.

mtomasek2 • Feb 26 '19

I'm using regex debuger, regexbuddy.com/, to debug different regex flavors. It saved me a lot of time over the years. It can also run on linux (using Wine).
They also have a tool for building regexps, regexmagic.com/, but I'm not using is so I'm just saying it is out there.

Thomas Junkツ • Feb 20 '19

For the day-to_day development, I recommend using Rubular or Regexly

Phillip Dodd • Feb 26 '19

Oh my, I wish that I had encountered this post about two months ago before I began the difficult journey of acquiring what (little) regex knowledge I have now... haha!

I'm absolutely going to be bookmarking this to revisit next time I have the need and will be sharing it with my team. You've laid this out in a very understandable way; thanks for sharing :)

Guillaume Duchemin • Apr 30 '19 • Edited

Thx a lot for this awesome cheat sheet !
You made a mistake in this case

const regexWithLetterAndNumberRange = /[a-z0-9]/ig;
const testString = "Emma19382";
testString.match(regexWithLetterAndNumberRange) // true

The result of match is // ["E", "m", "m", "a", "1", "9", "3", "8", "2"] ;)

Leonardo Galante • Feb 25 '19

Great cheat sheet, thank you Emma! Soon I'm gonna make a post about this extension I made for VSCode that could help understanding RegExp: marketplace.visualstudio.com/items...

Mehdi Vasigh • Feb 19 '19

Great post and doubles as a great practice assessment if you hide all of the code blocks!

Bartosz Maciejewicz • Feb 20 '19

I <3 it :) thank you very much :)

plainJavaScript • Feb 20 '19

Pretty fine.

I'mAHopelessDev • Feb 20 '19

very neat, thanks!

Sohail Nasir • Feb 19 '19

Thanks, this makes regex less scary! Keep up the good work

mmeyers00 • Feb 25 '19

Shouldn't this also go under #regex?

Lundeee • Feb 23 '19

Never ever did i wrote single regex without some kind of cheatsheet or tool. Thank you.

monsterooo • Feb 19 '19

⛄️

Phil Ashby • Jun 20 '19

Nicely done :)

Always choose carefully when choosing to use a regular expression of course. Our primary application at work is for input validation, drawing heavily on the excellent work done in OWASP: owasp.org/index.php/OWASP_Validati...

Saúl Blanco Tejero • Feb 20 '19

I love regexp 😊

Vinicius Dutra • Feb 21 '19

thanks for share this useful tips

Elango Sundar • Feb 25 '19

Nicely explained....!

websiteworkshop • Feb 20 '19

Thank you for making such a clear reference

LuisPa • Feb 27 '19

Great post Emma!

Jon Randy 🎖️ • Feb 22 '19

Best regex cheatsheet I ever came across - appletree.or.kr/quick_reference_ca...

Aditya Sharan • Oct 4 '20

I think you forgot to put what is the meaning of "gi" or "ig" in regular expression
For other folks out there
g modifier: global. All matches (don't return on first match)
i modifier: insensitive. Case insensitive match (ignores case of [a-zA-Z])

Shah Nawaz Shuvo • Feb 25 '19

This is a great reference guide. Thank you Emma

Jackson Elfers • Feb 20 '19

There are definitely some regex wizards out there, great work putting this together. 😁

Jesse • Feb 26 '19

Cannot get enough of these :D... because regex is something that I have to lookup no matter how many times I use it.

Tutlane • Feb 26 '19

Thanks emma for the list, will share it in our JavaScript topics.

David Joseph Kamer • Feb 25 '19

I've mostly used .test, but you make good use of the .match method. Thanks for the great regex post with a JavaScript focus!

Gaurav Lonkar • May 25 '19

Can anyone help me in writting regex for accepting google.com, yahoo.com, youtube.com but not sites.google.com translate.google.com m.youtube.com admin.yahoo.com etc

Aranganathan • Mar 31 '19

wow stuff !

cyr1l • Jun 12 '19

Great cheat sheet! Regex tester for JavaScript: extendsclass.com/regex-tester.html

Max Cerrina • Apr 29 '19

I love this, and what I really love is that you used super great and clear variable names!

faizee • Apr 29 '19

Finally I understand hoe regular expressions works

Herat Patel • Aug 25 '19

Thanks, very helpful...!

Se-ok Jeon • Sep 24 '21

Thx for your great post. it helped me a lot. If you don't mind, Can I translate this post into Korean? Surely, there will be a link at top of my post directing to this original post.