Scala Process - Capture Standard Out and Exit Code

Question

I'm working with the Scala scala.sys.process library.

I know that I can capture the exit code with ! and the output with !! but what if I want to capture both?

I've seen this answer https://stackoverflow.com/a/6013932/416338 which looks promising, but I'm wondering if there is a one liner and I'm missing something.

Answer 1

I have the following utility method for running commands:

import sys.process._
def runCommand(cmd: Seq[String]): (Int, String, String) = {
  val stdoutStream = new ByteArrayOutputStream
  val stderrStream = new ByteArrayOutputStream
  val stdoutWriter = new PrintWriter(stdoutStream)
  val stderrWriter = new PrintWriter(stderrStream)
  val exitValue = cmd.!(ProcessLogger(stdoutWriter.println, stderrWriter.println))
  stdoutWriter.close()
  stderrWriter.close()
  (exitValue, stdoutStream.toString, stderrStream.toString)
}

As you can see, it captures stdout, stderr and result code.

Answer 2

You can use ProcessIO. I needed something like that in a Specs2 Test, where I had to check the exit value as well as the output of a process depending on the input on stdin (in and out are of type String):

"the operation" should {
  f"return '$out' on input '$in'" in {
    var res = ""
    val io = new ProcessIO(
      stdin  => { stdin.write(in.getBytes)
                  stdin.close() }, 
      stdout => { res = convertStreamToString(stdout)
                  stdout.close() },
      stderr => { stderr.close() })
    val proc = f"$operation $file".run(io)
    proc.exitValue() must be_==(0)
    res must be_==(out)
  }
}

I figured that might help you. In the example I am ignoring what ever comes from stderr.

Answer 3

You can specify an output stream that catches the text:

import sys.process._
val os   = new java.io.ByteArrayOutputStream
val code = ("volname" #> os).!
os.close()
val opt  = if (code == 0) Some(os.toString("UTF-8")) else None

Answer 4

The one-line-ish use of BasicIO or ProcessLogger is appealing.

scala> val sb = new StringBuffer
sb: StringBuffer = 

scala> ("/bin/ls /tmp" run BasicIO(false, sb, None)).exitValue
res0: Int = 0

scala> sb
res1: StringBuffer = ...

or

scala> import collection.mutable.ListBuffer
import collection.mutable.ListBuffer

scala> val b = ListBuffer[String]()
b: scala.collection.mutable.ListBuffer[String] = ListBuffer()

scala> ("/bin/ls /tmp" run ProcessLogger(b append _)).exitValue
res4: Int = 0

scala> b mkString "\n"
res5: String = ...

Depending on what you mean by capture, perhaps you're interested in output unless the exit code is nonzero. In that case, handle the exception.

scala> val re = "Nonzero exit value: (\\d+)".r.unanchored
re: scala.util.matching.UnanchoredRegex = Nonzero exit value: (\d+)

scala> Try ("./bomb.sh" !!) match {
     | case Failure(f) => f.getMessage match {
     |   case re(x) => println(s"Bad exit $x")
     | }
     | case Success(s) => println(s)
     | }
warning: there were 1 feature warning(s); re-run with -feature for details
Bad exit 3

Answer 5

The response provided by 'Alex Cruise' in your link is fairly concise, barring poorer performance.

You could extend sys.process.ProcessLogger to manage the

var out = List[String]()
var err = List[String]()

internally, with getters for the out.reverse and err.reverse results.

Answer 6

Here's a really simple Scala wrapper that allows you to retrieve stdout, stderr and exit code.

import scala.sys.process._

case class ProcessInfo(stdout: String, stderr: String, exitCode: Int)

object CommandRunner {

def runCommandAndGetOutput(command: String): ProcessInfo = {
    val stdout = new StringBuilder
    val stderr = new StringBuilder
    val status = command ! ProcessLogger(stdout append _, stderr append _)
    ProcessInfo(stdout.toString(), stderr.toString(), status)
  }
}

Answer 7

I combined these and came up with this. The expected RC is there because I have a program I need to run in one project that returns 1 when it works. This does depend on the text of the Exception, but it will still do something reasonable it that doesn't match.

  private val ProcessErrorP: Regex = "(.*): error=(\\d+),(.*)".r.unanchored

  case class ProcessInfo(stdout: String, stderr: String, exitCode: Int, private val expectedRd: Int) {
    def succeeded: Boolean = exitCode == expectedRd
    def failed: Boolean = !succeeded
    def asOpt: Option[String] = if (succeeded) None else Some(stderr)
  }

  /**
   * Run a simple command
   * @param command -- what to run
   * @return -- what happened
   */
  def run(command: String, expectedRc: Int = 0): ProcessInfo = {
    try {
      val stdout = new StringBuilder
      val stderr = new StringBuilder
      val status = command ! ProcessLogger(stdout append _, stderr append _)
      ProcessInfo(stdout.toString(), stderr.toString(), status, expectedRc)
    } catch {
      case io: IOException =>
        val dm = io.getMessage
        dm match {
          case ProcessErrorP(message, code, reason) =>
            ProcessInfo("", s"$message, $reason", code.toInt, expectedRc)
          case m: String =>
            ProcessInfo("", m, 999, expectedRc)
        }
    }
  }