How do you regex?

I made a thread yesterday called How do you feel about regex?

Lots of fun discussion. Lots of people weighed in on their tools and tactics, but I'd love to move the conversation that way.

How do you go about using regex.

• What tools do you use? (if not from full memory)
• How do you encapsulate/label/comment regex?
• What types of problems do you most solve with regex?

Looking forward to any and all comments!

Comments

[Waylon Walker]

I regex in all the terminal dev tools vim, nvim, grep, ag, rg.

[Ben Halpern]

For Ruby regex I've always used Rubular as a lightweight reference tool. I do much more from knowledge/memory than I used to, but I'm still mostly a user of search and tools like this for anything complicated.

[Sherry Day]

I like this approach from the other thread

Jeremy Friesen • Jan 4

I love using regular expressions. And try to adopt the following pattern:

1. Write a method for evaluating the regular expression.
2. Bombard that method with tests, both matching and non-matching cases.
3. Profit!

Regular expressions can be quite dense to read, so I want to use the tests to highlight my expectations around what I wrote.

[Daniel Starner]

For building & explaining regular expressions, I always use regex101.com/. It's a great tool that really break down how your regular expression will work, which is very useful if it can get complex. It also has multi-language support to match the regex flavors across different major languages & distributions.

For learning regex, I usually just Google and dive through StackOverflow posts similar to what I'm trying to do. If I write a regex that is more complicated than just some alphanumeric grouping, I try to comment it with some human text such as capture the ID from the post slug or something of the sorts...not very in-depth, but 😅

Regular expressions are most commonly used when I am validating string structure, which could be form inputs, hostname information, or CSV data. If I am parsing strings, my first go-to for basic cases is to do some combination of .split() and .join on the resulting array, as its a bit easier to reason about and requires no understanding of regular expressions, just some basic logic. I tend to fall back to regular expressions if the string parsing is more complicated, has more than one match, or requires some more advanced substitution.

[Ben Halpern]

For learning regex, I usually just Google and dive through StackOverflow posts similar to what I'm trying to do.

Just curious, have you ever considered taking on a dedicated approach to learning Regex — like a book or course?

Definitely not a judgment, just a curiousity.

[Daniel Starner]

No judgements found!

I tend to learn on the fly as I'm trying to implement something, so it probably means I am going to immediately use the idea if I am learning something new concerning regular expressions. This is also predicated on the fact that I've been using them with regular consistency for 4-5 years so I have a firm foundation in the basics. If I am looking something up, its usually related to Named Groups (I always forget the exact syntax), Lookarounds, and Conditions. The latter two only get used in very rare & complex scenarios, so I don't bother committing them to memory fully.

When I was just getting started, I just spent a day on regex101.com/ trying to build different expressions to match different strings to see how it would work. This learning was compounded by the fact that Django used to exclusively use regular expressions for route matching, so it "forced" me to work with them.

[Piyush Kumar Baliyan]

I use Regexr (regexr.com) to quickly test out my regexes. It supports JS style regex. and is very handy since it has features like live preview, and explanation of your regex.

For explaining regex, I mostly try to create simple and small regex, and assign it to some const (or function) to make it understandable.
e.g. I'll never do if (/regex/.test(str)), but always const EMAIL_REGEX = /regex/, and then my code.

For solving problems, I use it to sometimes modify data structures on the fly, and code refactor.
I also recently wrote a post about it: dev.to/admitkard/regexp-cheatsheet...

RegExp Cheatsheet to speed up code editing and refactor

Piyush Kumar Baliyan for AdmitKard ・ Jan 4 ・ 5 min read

#javascript #vscode #regex #webdev

[DevFranPR]

This VSC plugin with a regex rules on another window is a life saver marketplace.visualstudio.com/items...

[Aleksandr Hovhannisyan]

I like using regexr.com/ to test my regex and make sure it behaves correctly for edge cases. It's a wonderful tool!

These days, I mainly use regex at the editor level (e.g., in VS Code) to mass-replace certain patterns with other patterns when it's not possible to easily rename them using built-in editor shortcuts. For example, in early 2021, I migrated my site from Jekyll to 11ty, and as part of that migration, I had to convert a bunch of my Liquid shortcodes to use a new syntax. Since I had hundreds of matches, I relied on regex to mass-replace them rather than doing it by hand.

More recently, I also learned about the HTML pattern attribute, which accepts any valid regex to validate a form input, and have been using it where appropriate for client-side validation. For example, in a recent project, I used the pattern ^[a-zA-Z0-9-](?:(,\s*)?[a-zA-Z0-9-])*$ to match a comma-separated list of identifiers, with potential spaces after the commas. It seemed difficult to arrive at this solution initially, but then I realized that it was just a more complex case of the slug regex pattern I used here: npmjs.com/package/is-slug.

While I find it easy to compose basic regex patterns, I do think it's harder to read regex, especially for complex patterns like the one above, and especially if I'm reading other people's regex.

[Corey McCarty]

If at all possible, avoid using regex in code. If you must include regex in code then you should make efforts to explain what the different parts do. All of that said, I have come across some examples of entry validation in front-end where the best approach was to request the validations from the back-end depending on the locale, and then pass back regex strings. This keeps you from having hard coded regex in the front-end, but means that the back-end has a plethora of regex patterns stored based on the field being validated and the locale. For this think of a list of phone number validation regexes by locale code being in one place. This is an attempt to prevent sending information to the back-end to perform validation, but as a safety precaution, the back-end should still perform the validation to insure that there's been no tampering with the validation steps.

When I use regex it is usually for searching in my code or local file system, and I use Regexr as both a reference and a test tool. One instance that I used during Advent of Code was to find any commented/uncommented print calls in the code before commit.

[Alex Lohr]

I just write them down; ,usually they work. I comment more complex RegExp by splitting up the parts of it in a comment, e.g. for a simple example:

// Matches cookies in document.cookie
// $1: key `([^=]+)` one or more not `=`
// separator `=`
// $2: value `([^;]+)` one or more not `;`
// Modifier 'g' (global)
const cookieMatcher = /([^=]+)=([^;]+)/g;

[Jeremy Friesen]

For tools, I like to use Ruby to write my regex. I often refer to the documentation. I invariably pair the regex with lots of local tests.

Below is a basic test. I save the code to a file (e.g. regexp.rb) and then run ruby regexp.rb.

THE_REGEX = %r{\d+}
def the_matcher(text)
  THE_REGEX.match?(text)
end

if __FILE__ == $0
  [
    ["123", true],
    ["abc", false],
  ].each do |text, expected|
    actual = the_matcher(text)
    if actual == expected
      puts "SUCCESS: for #the_matcher(#{text.inspect})"
    else
      puts "FAILURE: Expected #the_matcher(#{text.inspect}) to return #{expected}, got #{actual}"
    end
  end
end

I favor these basic tests as I'm writing regular expressions as they are super fast to run. And are easy to later port into the test suite of the application (which depending on how the application tests are constructed might be faster or slower to run).

For types of problems, I've used it for:

• Creating a command line REPL for facilitating note taking/random tables in RPGs.
• For tidying up my text before writing a Forem Pull Requests
• For parsing/tokenizing strings
• For pruning my local git branchs when the upstream tracking branch goes away.
• For building a stats task for lines of code in an application

[GrahamTheDev]

Well I did use regex quite heavily to build a basic JS syntax highlighter (instead of doing it properly with tokenisation)

Other than that I just tend to use them for validation of input!

[Derek Enos]

I usually work from memory and try to use as many named capturing groups as possible because I find that it serves to provide basic, inline, documentation of the pattern itself, and provides a more expressive way of accessing the groups on the match result:

const regex = /(?<first>[^\-])-(?<second>[^\-])-(?<rest>.+)/

const { groups } = regex.exec("1-2-3-4-5")

groups.first
'1'
groups.second
'2'
groups.rest
'3-4-5'

[Calin Baenen]

• What tools do you use? (if not from full memory)

regex101, as stated yesterday.
Otherwise I try to do things from memory, or look shiz up.

• How do you encapsulate/label/comment regex?

I don't.

• What types of problems do you most solve with regex?

ParseJS with "abstract tokens", that'd allow for you to make a programming language with usable identifiers.

[scottshipp]

Some people, when confronted with a problem, think 'I know, I’ll use regular expressions.' Now they have two problems.

—Jamie Zawinski

Hence, I only use regex when I have to. And I usually just end up using the built-in language features for it.

[Vicente G. Reyes]

I wrote(WIP) an article which I shared with my colleagues which explains regex. These colleagues have little to no knowledge on how regex works hence the urge to write and help them get started using it since we're the last people who work on clients' project before giving it back to them. Our work includes making sure the data's clean and consistent. notion.so/vicentereyes/Introductio...