Capturing after the nth occurrence of a string using regex

Question

My test string:

/custom-heads/food-drinks/51374-easter-bunny-cake

I am trying to capture the number in the string. The constants in that string are the the number is always preceded by 3 /'s and followed by a -.

I am a regex noob and am struggling with this. I cobbled together (\/)(.*?)(-) and then figured I could get the last one programmatically, but I would really like to understand regex better and would love if someone could show me the regex to get the last occurrence of numbers between / and -.

Maielo · Accepted Answer · 2022-04-12 21:16:27Z

2

Don't use regexes if possible, i reccomend you to read - https://blog.codinghorror.com/regular-expressions-now-you-have-two-problems/ blog post

To your question, its easier, faster, more bullet proof to get it using splits

const articleName = "/custom-heads/food-drinks/51374-easter-bunny-cake".split("/")[3]
// '51374-easter-bunny-cake'

const articleId = articleName.split("-")[0]

// '51374'

hope it helps

answered Apr 12, 2022 at 21:16

Maielo

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1 Comment

anubhava Over a year ago

2 operations: .split("/")[3] followed by .split("-")[0] is equivalent of /^(?:[^\/]*\/){3}([^-]+)/

anubhava · Accepted Answer · 2022-04-12 21:19:31Z

0

You may use this regex with a capture group:

^(?:[^\/]*\/){3}([^-]+)

Or in modern browsers you can use lookbehind assertion:

/(?<=^(?:[^\/]*\/){3})[^-]+/

RegEx Demo 1

RegEx Demo 2

RegEx Code:

^: Start
(?:[^\/]*\/){3}: Match 0 or more non-/ characters followed by a /. Repeat this group 3 times
([^-]+): Match 1+ of non-hyphen characters

Code:

const s = `/custom-heads/food-drinks/51374-easter-bunny-cake`;

const re = /^(?:[^\/]*\/){3}([^-]+)/;

console.log (s.match(re)[1]);

edited Apr 12, 2022 at 21:19

answered Apr 12, 2022 at 21:09

anubhava

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2 Comments

S16 Over a year ago

This is really close. Only issue is that it matches all the text before the number as well as the number. How do I omit that first group from the match?

anubhava Over a year ago

That's why we use capture group for number. Modern Javascript uses lookbehind so you can use: /(?<=^(?:[^\/]*\/){3})[^-]+/

Ryszard Czech · Accepted Answer · 2022-04-12 21:23:12Z

Use

const str = `/custom-heads/food-drinks/51374-easter-bunny-cake`
const p = /(?:\/[^\/]*){2}\/(\d+)-/
console.log(str.match(p)?.[1])

See regex proof.

EXPLANATION

Non-capturing group (?:\/[^\/]*){2}
{2} matches the previous token exactly 2 times
\/ matches the character / with index 4710 (2F16 or 578) literally (case sensitive)
  Match a single character not present in the list below [^\/]
  * matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
  \/ matches the character / with index 4710 (2F16 or 578) literally (case sensitive)
\/ matches the character / with index 4710 (2F16 or 578) literally (case sensitive)
1st Capturing Group (\d+)
  \d matches a digit (equivalent to [0-9])
  + matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
- matches the character - with index 4510 (2D16 or 558) literally (case sensitive)

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