ZIO learning - playing with streams - stream based grep implementation / published by https://github.com/dacr/code-examples-manager #32c91a86-e72f-42ae-878d-5cd8e68935d5/7d0900d2f9c483009c65f524e5ae94865acb7c1a

zio-learning-streams-2-grep.sc

// summary : ZIO learning - playing with streams - stream based grep implementation
// keywords : scala, zio, learning, streams, grep
// publish : gist
// authors : zio
// license : Apache License Version 2.0 (https://www.apache.org/licenses/LICENSE-2.0.txt)
// id : 32c91a86-e72f-42ae-878d-5cd8e68935d5
// created-on : 2021-10-30T23:09:55+02:00
// managed-by : https://github.com/dacr/code-examples-manager
// run-with : scala-cli $file
// usage-example : scl zio-learning-streams-2-grep.sc -- '.*getArgs' zio-learning-streams-2-grep.sc

// ---------------------
//> using scala "3.4.2"
//> using dep "dev.zio::zio:2.0.13"
//> using dep "dev.zio::zio-streams:2.0.13"
// ---------------------
import zio.*
import zio.stream.*

import java.nio.file.Paths
import zio.stream.ZPipeline.{splitLines, utf8Decode}
import scala.util.matching.Regex

object Grep extends ZIOAppDefault {

  def grepStream(inputFile: String, regex: Regex) =
    ZStream
      .fromFile(Paths.get(inputFile).toFile)
      .via(utf8Decode >>> splitLines)
      .filter(line => regex.findFirstIn(line).isDefined)

  val run =
    for {
      args         <- getArgs
      pattern      <- ZIO.from(args.headOption).tapError(_ => Console.printLine("grep pattern not provided"))
      filename     <- ZIO.from(args.drop(1).headOption).tapError(_ => Console.printLine("grep filename not provided"))
      regex        <- ZIO.attempt(pattern.r)
      foundResults <- grepStream(filename, regex).runCollect
      _            <- ZIO.foreach(foundResults)(matchingLine => Console.printLine(matchingLine))
    } yield ()
}

Grep.main(args)