Kotlin: Find the first line of a file that matches a regex, and return captured values - kotlin

Question

i want get text from a file by using regEx and want save the file with a new name (using the results of the regEx-Find).
My Problem is that i cant get/return the correct genearated (in this example xyz maur) out of the function readFileLineByLineUsingForEachLine(fileName: String) the new newFileName which was generated (sucessfully as expected) in the function.
Line 1 of Source:
start {"Name":"xyz","Civ":"maur","Team":0}
My Prototype:
fun main() {
val f = "./commands.txt";
var newFileName = readFileLineByLineUsingForEachLine(f)
print(newFileName.)
val source = Paths.get(f)
val target = Paths.get("/home/x/snap/0ad/199/.local/share/0ad/replays/0.0.24/2021-03-14_0016/" + newFileName)
// try {
// val move = Files.move(
// source,
// target
// )
// } catch (e: IOException) {
// e.printStackTrace()
// }
};
fun readFileLineByLineUsingForEachLine(fileName: String) // https://www.baeldung.com/kotlin/read-file
= File(fileName).forEachLine lit#{
// "Name":"Cleisthenes"
val regexString = """
"Name":(?<Name>"\w+").*?"Civ":(?<Civ>"\w+").*?"Team":0
""".trim()
var regex = Regex(regexString)
var matched = regex.find(it)?.groupValues
val Name = matched?.get(1)
val Civ = matched?.get(2)
if (Name != null)
println(Name)
if (Civ != null)
println(Civ)
val newFileName = "$Name $Civ"
return#lit
}

Answer 1

Because you want to stop processing as soon as you find a match, I don't think forEachLine is the best choice. Instead you can use useLines, and combine it with first to stop processing once you get a match:
val regex = Regex(""""Name":(?<Name>"\w+").*?"Civ":(?<Civ>"\w+").*?"Team":0""")
fun readFileLineByLineUsingForEachLine(fileName: String) =
File(fileName).useLines { lines ->
val (name, civ) = lines
.map { regex.find(it) }
.filterNotNull()
.first()
.destructured
"$name $civ"
}
For the example you provided, this returns the string "xyz" "maur".

Answer 2

that's just a very little modification of the correct, helpful answer from Adam here https://stackoverflow.com/a/66654710/2891692
fun readFileLineByLineUsingForEachLine2(fileName: String) =
File(fileName).useLines { lines ->
val (name, civ) = lines
.map {
val regexString = """
"Name":(?<Name>"\w+").*?"Civ":(?<Civ>"\w+").*?"Team":0
""".trim()
var regex = Regex(regexString)
regex.find(it)
}
.filterNotNull()
.first()
.destructured
"$name $civ"
}