Cheatsheet for the Regex Cheatsheet, Part VI: Escape Sequences

Intro

I was recently doing a code challenge for a job interview that required me to strip out all nonalphabetic characters. “Ah! I should use Regular Expressions for this!” I thought in triumph, impressed that I even knew what regular expres…


This content originally appeared on DEV Community and was authored by Analogy | Absence | Example

Intro

I was recently doing a code challenge for a job interview that required me to strip out all nonalphabetic characters. "Ah! I should use Regular Expressions for this!" I thought in triumph, impressed that I even knew what regular expressions were. That fleeting moment of glory faded once I decided to brush up on regular expressions and landed on the encouragingly-named Regular Expressions Cheatsheet. I had no idea how to use it!

So, for people like me, here is a Cheatsheet for the Regular Expressions Cheatsheet, Part VI: Escape Sequences

Alt Text

What's an Escape Sequence?

Regular Expressions are typically used to search for characters or sequences of characters. This process is straightforward for a regular character such as a number or letter, but what if you're searching for a character that has special meaning in code, such as an *? To tell the interpreter that you mean the literal character * instead of the wildcard property of *, you "escape" the character by placing a \ in front of it.

Anatomy of a regular expression

  1. Forward slashes go on either end like so: /something/
  2. Add g for "global" at the end to find every instance, like so: /something/g
  3. Add m to "multi line" to the beginning/end of each line, not just the beginning/end of each string, like /something/g or /something/gm

Escape Sequences

I'm going to illustrate the next few concepts with Mozilla's exceptionally clever wordmark, which is moz:\\a
Alt Text

\ Escape following character
  • \ is used in \/\// to find the following: Mozilla's wordmark is moz://a
  • Example on regex101.com
  • Example in Javascript: 
let sentence = "Mozilla's wordmark is moz://a";
let regex = \/\//;
let found = sentence.match(regex);
console.log(found); // [
  '//',
  index: 26,
  input: "Mozilla's wordmark is moz://a",
  groups: undefined
]

Ok, but what if Mozilla changed their wordmark from moz://a to moz:\\a?

Let's try it that way...

  • \ is used in /\\/ to find the following: "What if Mozilla changed their wordmark from moz://a to moz:\\a?"
  • Example on regex101.com:
    • For some strange reason, on regex101 /\\/ will only find the first \, see example.
    • To find both \\, the regex needs to be /\\\\/, see example
  • Example in Javascript:

(Note: To make this work, the string needs to spell the wordmark as moz:\\\\a)

let sentence = "What if Mozilla changed their wordmark from moz://a to moz:\\\\a?";
let regex = /\\/;
let found = sentence.match(regex);
console.log(sentence); // What if Mozilla changed their wordmark from moz://a to moz:\\a?
console.log(found); // [
  '\\',
  index: 59,
  input: 'What if Mozilla changed their wordmark from moz://a to moz:\\\\a?',
  groups: undefined
]

Well, I think we now know why Mozilla went with moz://a instead of moz:\\a!"

Regex Escape Sequences that are not supported in Javascript

\Q Begin literal sequence
\E End literal sequence


This content originally appeared on DEV Community and was authored by Analogy | Absence | Example


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