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I am confusing about how to make any regular expressions. e.g I have to make the regular expression of this type of string,

fetch/https://upload.wikimedia.org/wikipedia/w_100/commons/f/f9/Phoenicopterus_ruber_in_São_Paulo_Zoo.jpg fetch/https://upload.wikimedia.org/wikipedia/w_100,h_100,fl_progressive,dpr_2.0/commons/f/f9/Phoenicopterus_ruber_in_São_Paulo_Zoo.jpg

so I want to match only frm first string w_100 and from second string w_100,h_100,fl_progressive,dpr_2.0 likewise different urls.

var regex = /[a-z]_[0-9a-z]/g;
var found = string.match(regex);

it shows me output something like,

["w_1","s_r","r_i","n_s"]

I want something like this

["w_100","h_100","fl_progressive","dpr_2.0",]

can anyone suggest me a regular expression for this.?

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6
  • [0-9a-z] should be [0-9a-z]+. You need 1 or more. Ideally both should have one or more option: /[a-z]+_[0-9a-z]+/g; Commented Feb 12, 2020 at 8:00
  • should be /[a-z]+_([a-z]+|[0-9]+\.(?=[0-9]+)/ Commented Feb 12, 2020 at 8:06
  • @Rajesh your answer gives me like this ["w_100", "hoenicopterus_ruber"] I don't want this. Commented Feb 12, 2020 at 8:13
  • @AZ_ Invalid regular expression: /[a-z]+_([a-z]+|[0-9]+\.(?=[0-9]+)/: Unterminated group Commented Feb 12, 2020 at 8:16
  • 1
    @Keval /[a-z]+_([a-z]+|[0-9]+\.(?=[0-9]+))/ there was a typo. Commented Feb 12, 2020 at 8:48

2 Answers 2

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You can use following regex

let str = '/https://upload.wikimedia.org/wikipedia/w_100,h_100,fl_progressive,dpr_2.0,ar_3:4,quality_auto:good,effect_auto_brightness,effect_auto_color:50,effect_green:-30/commons/f/f9/Phoenicopterus_ruber_in_São_Paulo_Zoo.jpg'

console.log(str.match(/([a-z]+_([a-z]+|[0-9]+(\.[0-9]+)?)(?=(,|\/)))/g))

Update for added requirement.

console.log(str.match(/([a-z]+(?:_|:|:-)?([a-z]+|[0-9]+(\.[0-9]+)?)(?=(,|\/)))+/g))
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5 Comments

see "hoenicopterus_ruber" is also there. thanks for the answer. I'll sort it out.
what's the rule behind including fl_progressive but not hoenicopterus_ruber?
fl_progressive is the query parameter in the string URL. SO I want to extract it. btw thank you. now it's working fine.!
if i change the string to upload.wikimedia.org/wikipedia/… now can you please change the regex according to the string?
updated regex is not working for upper example. can you please check and fix it?
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The reason you have three characters matching for each match is because when you use the square brackets '[]', you are matching a single character from a possible range of characters. So your regex is currently looking for anything that has an alphabetic character between a-z, followed by an underscore, and finally another character between 0-9 or a-z.

To match multiple characters, you can add an asterisk '+' quantifier, which says the bit of regex that it is added to should match 1 or more times.

So to get the full matches, you can use the following: /[a-z]+_[0-9a-z.]+/g

However, this will also match hoenicopterus_ruber which is in the URLs.

To get around this issue, you can use a positive lookbehind:

(?<=wikipedia\/|,)[a-z]+_[0-9a-z.]+

NOTE: I've made the assumption that the URLs you are parsing are all wikipedia ones. If they are not, then you will need another solution for the second issue.

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it's just a format for my request URL, it should be anything like name.jpg, but if in case image name like name_like_this.jpg then it should not be matched with regex.

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