Strip paragraph text before cue word

Question

I have a text like this:

Last login: today


cat file
testMachine:root:/root# cat file
File contents
testMachine:root:/root#

And I need to retrieve the information like this:

testMachine:root:/root# cat file
File contents

Stripping away the last line is easy, but the amount of lines I need to remove at start is arbitrary, and I need to remove everything up until the first cue word, which is the machine name, that is known and stored.

I have tried substring() but it strips line by line instead of treating the whole text as one, and removes the host name too, which should remain there. I tried replace() too, but I am not familiar with regex, so the result is a memory exception.

EDIT 1: It seems to be important to note that using a JS for Java engine (In this case I'm using Rhino) means the result isn't the same as you get in web. This was found out after an answer below, which works perfectly on web, doesn't even run on the desktop app.

Answer 1

const text = ` 
Last login: today


cat file
testMachine:root:/root# cat file
File contents
testMachine:root:/root#`;
const cueWord = "testMachine:root"
const idx = text.indexOf(cueWord);
let restOftheString = text.substring(idx).split("\n");
restOftheString.pop()
console.log(restOftheString.join("\n"))