How to specify regex for route on content processor in NiFi?

Question

In nifi, I am routing based on content. I am using nifi's RouteOnContent So, how can I route by specifying the regex

My input content is:

{
"testreg":{
"test1":"test2",
"test3":"test4"
}
}

I wanted to test whether testreg whole content(word) present in the flowfile content. So, I checked with

1. testreg
2. (testreg)
3. .*testreg.*
4. (.*testreg.*)

But it is not matching with content, So, what is the correct regex to be used in Nifi.

Answer 1

Edit: It'ld make very much sense to check if the pattern we are looking for is surrounded by quotes and followed by a colon, since the patern testreg can simply occur somewhere else too. In this case we get the last match, which is not OK. So, eventually, this:

[\s\S]*?(?<=")(testreg)(?=":)[\s\S]*?

would be the ideal answer that we are looking for.

---

Maybe, here we want to have an expression that would pass the new lines. I'm not so sure what our desired output would be, however we can start testing against a few options, such as these expressions:

[\s\S]*(testreg)[\s\S]*

---

[\w\W]*(testreg)[\w\W]* 

---

[\d\D]*(testreg)[\d\D]*

---

([\s\S].*?)(testreg)?

---

Demo

This demo shows that we can capture and return our desired testreg:

const regex = /[\s\S]*(testreg)[\s\S]*/gm;
const str = `{
"testreg":{
"test1":"test2",
"test3":"test4"
}
}`;
const subst = `$1`;

// The substituted value will be contained in the result variable
const result = str.replace(regex, subst);

console.log('Substitution result: ', result);