Regex to match content between string that doesn't include this string

Question

I need to match a string that start end end with a specific string like [#start, and ,#end]. I use for that the regex /\[#start,(.*?),#end\]/g:

const string = '[#start,foobar,#end]'
const regex = /\[#start,(.*?),#end\]/g

console.log(string.match(regex))

The next step is to add the condition that the match doesn't contains in the middle another match like for example [#start,[#start,foobar,#end],#end]. I use for that a negative look-arounds /\[#start,((?!\[#start,(.*?),#end\]).*?),#end\]/g:

const string = '[#start,[#start,foobar,#end],#end]'
const regex = /\[#start,((?!\[#start,(.*?),#end\]).*?),#end\]/g

console.log(string.match(regex)) // --> will just match "[#start,foobar,#end]"

It's working well so far but the issue is that the start string is little bit more complex because it as to match something like /"#for (.*?) in (.*?)",/g. Example:

const string = '"#for i in [1, 2]",{"id": "[i]"},"#endfor"'
const regex = /"#for (.*?) in (.*?)",(.*?),"#endfor"/g

console.log([...string.matchAll(regex)])

Again I don't want that the 'middle' contains this syntax so I use like the previous example a negative look-arounds "#for (.*?) in (.*?)",(((?!"#for (.*?) in (.*?)",(.*?),"#endfor").)*?),"#endfor":

const string = '"#for i in [1, 2]","#for i in [1, 2]",{"id": "[i]"},"#endfor","#endfor"'
const regex = /"#for (.*?) in (.*?)",(((?!"#for (.*?) in (.*?)",(.*?),"#endfor").)*?),"#endfor"/g

console.log(string.match(regex))

But in this case it still match the first occurance of #for i in [1, 2] instead of just the string in the middle "#for i in [1, 2]",{"id": "[i]"},"#endfor". Any idea what is happening?

For those who wonder why such a regex, I need to use it in the development of the project restapify that enable you to easily mock a rest API with a JSON file structure.

anubhava · Accepted Answer · 2021-06-23 19:52:22Z

1

You may use this regex:

#for ((?:(?!#for .*? in .*?",|"#endfor).)*?) in ((?:(?!#for .*? in .*?",|"#endfor).)*?)",((?:(?!#for .*? in .*?",|"#endfor).)*?),"#endfor

RegEx Demo

Code:

const string = '"#for i in [1, 2]","#for i in [1, 2]",{"id": "[i]"},"#endfor","#endfor"';

const regex = /#for ((?:(?!#for .*? in .*?",|"#endfor).)*?) in ((?:(?!#for .*? in .*?",|"#endfor).)*?)",((?:(?!#for .*? in .*?",|"#endfor).)*?),"#endfor/g;

var m = [...string.matchAll(regex)]

if (m)
  console.log(m[0]);

edited Jun 23, 2021 at 19:52

answered Jun 23, 2021 at 14:50

anubhava

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5 Comments

johannchopin Over a year ago

Thanks for your help but here it should only match the string "#for i in [1, 2]",{"id": "[i]"},"#endfor" because it doesn't contain another #for ... syntax. In your example the first occurenance of #for i in [1, 2] is matched and that shouldn't be the case.

johannchopin Over a year ago

Thanks a lot for your help. Just a tiny question. With my first regex /"#for (.*?) in (.*?)",(.*?),"#endfor"/g, I'm able with the matchAll method to get all the different components of my string (see my example in the updated question). Sadly with yours I only get the middle part. Do you have any idea what I need to update to have all the 3 different parts? :)

anubhava Over a year ago

What are the expected matches for const string = '"#for i in [1, 2]","#for i in [1, 2]",{"id": "[i]"},"#endfor","#endfor"';? We can get same with my regex also by using:

#for ((?:(?!#for .*? in .*?",|"#endfor).)*?) in ((?:(?!#for .*? in .*?",|"#endfor).)*?)",((?:(?!#for .*? in .*?",|"#endfor).)*?),"#endfor

johannchopin Over a year ago

You can see if you run the third code snippet that you got in the console multiple elements according to the multiple (.*?). With this string the result should be ["\"#for i in [1, 2]\",{\"id\": \"[i]\"},\"#endfor\"", "i", "[1, 2]", "{\"id\": \"[i]\"}"] but with yours regex I got ["#for i in [1, 2]\",{\"id\": \"[i]\"},\"#endfor", "{\"id\": \"[i]\"}". Any idea?

anubhava Over a year ago

You can see demo with my suggested regex. This shows your expected output.

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