scala.sys.process.ProcessLogger

trait ProcessLogger extends AnyRef

Encapsulates the output and error streams of a running process. This is used by scala.sys.process.ProcessBuilder when starting a process, as an alternative to scala.sys.process.ProcessIO, which can be more difficult to use. Note that a ProcessLogger will be used to create a ProcessIO anyway. The object BasicIO has some functions to do that.

Here is an example that counts the number of lines in the normal and error output of a process:

import scala.sys.process._

var normalLines = 0
var errorLines = 0
val countLogger = ProcessLogger(line => normalLines += 1,
                                line => errorLines += 1)
"find /etc" ! countLogger

Abstract Value Members From scala.sys.process.ProcessLogger

abstract def buffer[T](f: ⇒ T): T

If a process is begun with one of these ProcessBuilder methods:

def !(log: ProcessLogger): Int
def !<(log: ProcessLogger): Int

The run will be wrapped in a call to buffer. This gives the logger an opportunity to set up and tear down buffering. At present the library implementations of ProcessLogger simply execute the body unbuffered.

(defined at scala.sys.process.ProcessLogger)

abstract def err(s: ⇒ String): Unit

Will be called with each line read from the process error stream.

(defined at scala.sys.process.ProcessLogger)

abstract def out(s: ⇒ String): Unit

Will be called with each line read from the process output stream. (defined at scala.sys.process.ProcessLogger)

Full Source:

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2003-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

package scala
package sys
package process

import java.io._

/** Encapsulates the output and error streams of a running process. This is used
  * by [[scala.sys.process.ProcessBuilder]] when starting a process, as an
  * alternative to [[scala.sys.process.ProcessIO]], which can be more difficult
  * to use. Note that a `ProcessLogger` will be used to create a `ProcessIO`
  * anyway. The object `BasicIO` has some functions to do that.
  *
  * Here is an example that counts the number of lines in the normal and error
  * output of a process:
  * {{{
  * import scala.sys.process._
  *
  * var normalLines = 0
  * var errorLines = 0
  * val countLogger = ProcessLogger(line => normalLines += 1,
  *                                 line => errorLines += 1)
  * "find /etc" ! countLogger
  * }}}
  *
  *  @see [[scala.sys.process.ProcessBuilder]]
  */
trait ProcessLogger {
  /** Will be called with each line read from the process output stream.
   */
  def out(s: => String): Unit

  /** Will be called with each line read from the process error stream.
   */
  def err(s: => String): Unit

  /** If a process is begun with one of these `ProcessBuilder` methods:
   *  {{{
   *    def !(log: ProcessLogger): Int
   *    def !<(log: ProcessLogger): Int
   *  }}}
   *  The run will be wrapped in a call to buffer.  This gives the logger
   *  an opportunity to set up and tear down buffering.  At present the
   *  library implementations of `ProcessLogger` simply execute the body
   *  unbuffered.
   */
  def buffer[T](f: => T): T
}

/** A [[scala.sys.process.ProcessLogger]] that writes output to a file. */
class FileProcessLogger(file: File) extends ProcessLogger with Closeable with Flushable {
  private val writer = (
    new PrintWriter(
      new BufferedWriter(
        new OutputStreamWriter(
          new FileOutputStream(file, true)
        )
      )
    )
  )
  def out(s: => String): Unit = writer println s
  def err(s: => String): Unit = writer println s
  def buffer[T](f: => T): T = f
  def close(): Unit = writer.close()
  def flush(): Unit = writer.flush()
}

/** Provides factories to create [[scala.sys.process.ProcessLogger]], which
 *  are used to capture output of [[scala.sys.process.ProcessBuilder]] commands
 *  when run.
 */
object ProcessLogger {
  /** Creates a [[scala.sys.process.ProcessLogger]] that redirects output to a `java.io.File`. */
  def apply(file: File): FileProcessLogger = new FileProcessLogger(file)

  /** Creates a [[scala.sys.process.ProcessLogger]] that sends all output, standard and error,
   *  to the passed function.
   */
  def apply(fn: String => Unit): ProcessLogger = apply(fn, fn)

  /** Creates a [[scala.sys.process.ProcessLogger]] that sends all output to the corresponding
   *  function.
   *
   *  @param fout  This function will receive standard output.
   *
   *  @param ferr  This function will receive standard error.
   */
  def apply(fout: String => Unit, ferr: String => Unit): ProcessLogger =
    new ProcessLogger {
      def out(s: => String): Unit = fout(s)
      def err(s: => String): Unit = ferr(s)
      def buffer[T](f: => T): T = f
    }
}