scala.sys.process.ProcessBuilder

trait ProcessBuilder extends Source with Sink

Represents a sequence of one or more external processes that can be executed. A ProcessBuilder can be a single external process, or a combination of other ProcessBuilder . One can control where a the output of an external process will go to, and where its input will come from, or leave that decision to whoever starts it.

One creates a ProcessBuilder through factories provided in scala.sys.process.Process ‘s companion object, or implicit conversions based on these factories made available in the package object scala.sys.process. Here are some examples:

```scala import scala.sys.process._

// Executes “ls” and sends output to stdout “ls”.!

// Execute “ls” and assign a Stream[String] of its output to “contents”. val contents = Process(“ls”).lineStream

// Here we use a Seq to make the parameter whitespace-safe def contentsOf(dir: String): String = Seq(“ls”, dir).!! ```

The methods of ProcessBuilder are divided in three categories: the ones that combine two ProcessBuilder to create a third, the ones that redirect input or output of a ProcessBuilder , and the ones that execute the external processes associated with it.

Combining ProcessBuilder

Two existing ProcessBuilder can be combined in the following ways:

  • They can be executed in parallel, with the output of the first being fed as input to the second, like Unix pipes. This is achieved with the #| method.
  • They can be executed in sequence, with the second starting as soon as the first ends. This is done by the ### method.
  • The execution of the second one can be conditioned by the return code (exit status) of the first, either only when it’s zero, or only when it’s not zero. The methods #&& and #|| accomplish these tasks.

Redirecting Input/Output

Though control of input and output can be done when executing the process, there’s a few methods that create a new ProcessBuilder with a pre-configured input or output. They are #< , #> and #>> , and may take as input either another ProcessBuilder (like the pipe described above), or something else such as a java.io.File or a java.io.InputStream . For example:

new URL("http://databinder.net/dispatch/About") #> "grep JSON" #>> new File("About_JSON") !

Starting Processes

To execute all external commands associated with a ProcessBuilder , one may use one of four groups of methods. Each of these methods have various overloads and variations to enable further control over the I/O. These methods are:

  • run : the most general method, it returns a scala.sys.process.Process immediately, and the external command executes concurrently.
  • ! : blocks until all external commands exit, and returns the exit code of the last one in the chain of execution.
  • !! : blocks until all external commands exit, and returns a String with the output generated.
  • lineStream : returns immediately like run , and the output being generated is provided through a Stream[String] . Getting the next element of that Stream may block until it becomes available. This method will throw an exception if the return code is different than zero – if this is not desired, use the lineStream_! method.

Handling Input and Output

If not specified, the input of the external commands executed with run or ! will not be tied to anything, and the output will be redirected to the stdout and stderr of the Scala process. For the methods !! and lines , no input will be provided, and the output will be directed according to the semantics of these methods.

Some methods will cause stdin to be used as input. Output can be controlled with a scala.sys.process.ProcessLogger – !! and lines will only redirect error output when passed a ProcessLogger . If one desires full control over input and output, then a scala.sys.process.ProcessIO can be used with run .

For example, we could silence the error output from lines_! like this:

val etcFiles = "find /etc" lines_! ProcessLogger(line => ())

Extended Example

Let’s examine in detail one example of usage:

import scala.sys.process._
"find src -name *.scala -exec grep null {} ;"  #|  "xargs test -z"  #&&  "echo null-free"  #||  "echo null detected"  !

Note that every String is implicitly converted into a ProcessBuilder through the implicits imported from scala.sys.process. These ProcessBuilder are then combined in three different ways.

  1. #| pipes the output of the first command into the input of the second command. It mirrors a shell pipe ( | ).
  2. #&& conditionally executes the second command if the previous one finished with exit value 0. It mirrors shell’s && .
  3. #|| conditionally executes the third command if the exit value of the previous command is different than zero. It mirrors shell’s || .

Finally, ! at the end executes the commands, and returns the exit value. Whatever is printed will be sent to the Scala process standard output. If we wanted to capture it, we could run that with !! instead.

Note: though it is not shown above, the equivalent of a shell’s ; would be ### . The reason for this name is that ; is a reserved token in Scala.

Note: the lines method, though deprecated, may conflict with the StringLike method of the same name. To avoid this, one may wish to call the builders in Process instead of importing scala.sys.process._ . The example above would be

import scala.sys.process.Process
Process("find src -name *.scala -exec grep null {} ;") #| Process("xargs test -z") #&& Process("echo null-free") #|| Process("echo null detected") !

Abstract Value Members From scala.sys.process.ProcessBuilder

abstract def !!(log: ProcessLogger): String

Starts the process represented by this builder, blocks until it exits, and returns the output as a String. Standard error is sent to the provided ProcessLogger. If the exit code is non-zero, an exception is thrown.

(defined at scala.sys.process.ProcessBuilder)

abstract def !!<(log: ProcessLogger): String

Starts the process represented by this builder, blocks until it exits, and returns the output as a String. Standard error is sent to the provided ProcessLogger. If the exit code is non-zero, an exception is thrown. The newly started process reads from standard input of the current process.

(defined at scala.sys.process.ProcessBuilder)

abstract def !(log: ProcessLogger): Int

Starts the process represented by this builder, blocks until it exits, and returns the exit code. Standard output and error are sent to the given ProcessLogger.

(defined at scala.sys.process.ProcessBuilder)

abstract def !<(log: ProcessLogger): Int

Starts the process represented by this builder, blocks until it exits, and returns the exit code. Standard output and error are sent to the given ProcessLogger. The newly started process reads from standard input of the current process.

(defined at scala.sys.process.ProcessBuilder)

abstract def lineStream(log: ProcessLogger): Stream[String]

Starts the process represented by this builder. The output is returned as a Stream that blocks when lines are not available but the process has not completed. Standard error is sent to the provided ProcessLogger. If the process exits with a non-zero value, the Stream will provide all lines up to termination and then throw an exception.

(defined at scala.sys.process.ProcessBuilder)

abstract def lineStream_!(log: ProcessLogger): Stream[String]

Starts the process represented by this builder. The output is returned as a Stream that blocks when lines are not available but the process has not completed. Standard error is sent to the provided ProcessLogger. If the process exits with a non-zero value, the Stream will provide all lines up to termination but will not throw an exception.

(defined at scala.sys.process.ProcessBuilder)

abstract def run(): Process

Starts the process represented by this builder. Standard output and error are sent to the console.

(defined at scala.sys.process.ProcessBuilder)

abstract def run(connectInput: Boolean): Process

Starts the process represented by this builder. Standard output and error are sent to the console. The newly started process reads from standard input of the current process if connectInput is true.

(defined at scala.sys.process.ProcessBuilder)

abstract def run(io: ProcessIO): Process

Starts the process represented by this builder. I/O is handled by the given ProcessIO instance.

(defined at scala.sys.process.ProcessBuilder)

abstract def run(log: ProcessLogger): Process

Starts the process represented by this builder. Standard output and error are sent to the given ProcessLogger.

(defined at scala.sys.process.ProcessBuilder)

abstract def run(log: ProcessLogger, connectInput: Boolean): Process

Starts the process represented by this builder, blocks until it exits, and returns the exit code. Standard output and error are sent to the given ProcessLogger. The newly started process reads from standard input of the current process if connectInput is true.

(defined at scala.sys.process.ProcessBuilder)

Deprecated Value Members From scala.sys.process.ProcessBuilder

abstract def !: Int

Starts the process represented by this builder, blocks until it exits, and returns the exit code. Standard output and error are sent to the console.

(defined at scala.sys.process.ProcessBuilder)

def lines(log: ProcessLogger): Stream[String]

Deprecated (renamed). Use lineStream(log: ProcessLogger) instead.

  • Annotations
    • @ deprecated
  • Deprecated
    • (Since version 2.11.0) Use stream instead.

(defined at scala.sys.process.ProcessBuilder)

def lines_!(log: ProcessLogger): Stream[String]

Deprecated (renamed). Use lineStream_!(log: ProcessLogger) instead.

  • Annotations
    • @ deprecated
  • Deprecated
    • (Since version 2.11.0) Use stream_! instead.

(defined at scala.sys.process.ProcessBuilder)

Abstract Value Members From scala.sys.process.ProcessBuilder

abstract def #&&(other: ProcessBuilder): ProcessBuilder

Constructs a command that runs this command first and then other if this command succeeds.

(defined at scala.sys.process.ProcessBuilder#)

abstract def #|(other: ProcessBuilder): ProcessBuilder

Constructs a command that will run this command and pipes the output to other . other must be a simple command.

(defined at scala.sys.process.ProcessBuilder#)

abstract def #||(other: ProcessBuilder): ProcessBuilder

Constructs a command that runs this command first and then other if this command does not succeed.

(defined at scala.sys.process.ProcessBuilder#)

Abstract Value Members From scala.sys.process.ProcessBuilder

abstract def ###(other: ProcessBuilder): ProcessBuilder

Constructs a command that will run this command and then other . The exit code will be the exit code of other .

(defined at scala.sys.process.ProcessBuilder####)

Abstract Value Members From scala.sys.process.ProcessBuilder.Sink

abstract def toSink: ProcessBuilder

  • Attributes
    • protected
  • Definition Classes
    • Sink

(defined at scala.sys.process.ProcessBuilder.Sink)

Concrete Value Members From scala.sys.process.ProcessBuilder.Sink

def #<(f: File): ProcessBuilder

Reads the given file into the input stream of this process.

  • Definition Classes
    • Sink

(defined at scala.sys.process.ProcessBuilder.Sink#)

def #<(b: ProcessBuilder): ProcessBuilder

Reads the output of a scala.sys.process.ProcessBuilder into the input stream of this process.

  • Definition Classes
    • Sink

(defined at scala.sys.process.ProcessBuilder.Sink#)

def #<(f: URL): ProcessBuilder

Reads the given URL into the input stream of this process.

  • Definition Classes
    • Sink

(defined at scala.sys.process.ProcessBuilder.Sink#)

def #<(in: ⇒ InputStream): ProcessBuilder

Reads the given InputStream into the input stream of this process. The argument is call-by-name, so the stream is recreated, read, and closed each time this process is executed.

  • Definition Classes
    • Sink

(defined at scala.sys.process.ProcessBuilder.Sink#)

Abstract Value Members From scala.sys.process.ProcessBuilder.Source

abstract def toSource: ProcessBuilder

  • Attributes
    • protected
  • Definition Classes
    • Source

(defined at scala.sys.process.ProcessBuilder.Source)

Concrete Value Members From scala.sys.process.ProcessBuilder.Source

def cat: ProcessBuilder

Returnes a scala.sys.process.ProcessBuilder representing this Source .

  • Definition Classes
    • Source

(defined at scala.sys.process.ProcessBuilder.Source)

Concrete Value Members From scala.sys.process.ProcessBuilder.Source

def #>(f: File): ProcessBuilder

Writes the output stream of this process to the given file.

  • Definition Classes
    • Source

(defined at scala.sys.process.ProcessBuilder.Source#)

def #>(b: ProcessBuilder): ProcessBuilder

Writes the output stream of this process to a scala.sys.process.ProcessBuilder.

  • Definition Classes
    • Source

(defined at scala.sys.process.ProcessBuilder.Source#)

def #>(out: ⇒ OutputStream): ProcessBuilder

Writes the output stream of this process to the given OutputStream. The argument is call-by-name, so the stream is recreated, written, and closed each time this process is executed.

  • Definition Classes
    • Source

(defined at scala.sys.process.ProcessBuilder.Source#)

def #>>(f: File): ProcessBuilder

Appends the output stream of this process to the given file.

  • Definition Classes
    • Source (defined at scala.sys.process.ProcessBuilder.Source#)

Full Source:

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

package scala
package sys
package process

import processInternal._
import ProcessBuilder._

/** Represents a sequence of one or more external processes that can be
  * executed. A `ProcessBuilder` can be a single external process, or a
  * combination of other `ProcessBuilder`. One can control where a
  * the output of an external process will go to, and where its input will come
  * from, or leave that decision to whoever starts it.
  *
  * One creates a `ProcessBuilder` through factories provided in
  * [[scala.sys.process.Process]]'s companion object, or implicit conversions
  * based on these factories made available in the package object
  * [[scala.sys.process]]. Here are some examples:
  * {{{
  * import scala.sys.process._
  *
  * // Executes "ls" and sends output to stdout
  * "ls".!
  *
  * // Execute "ls" and assign a `Stream[String]` of its output to "contents".
  * val contents = Process("ls").lineStream
  *
  * // Here we use a `Seq` to make the parameter whitespace-safe
  * def contentsOf(dir: String): String = Seq("ls", dir).!!
  * }}}
  *
  * The methods of `ProcessBuilder` are divided in three categories: the ones that
  * combine two `ProcessBuilder` to create a third, the ones that redirect input
  * or output of a `ProcessBuilder`, and the ones that execute
  * the external processes associated with it.
  *
  * ==Combining `ProcessBuilder`==
  *
  * Two existing `ProcessBuilder` can be combined in the following ways:
  *
  *   - They can be executed in parallel, with the output of the first being fed
  *     as input to the second, like Unix pipes. This is achieved with the `#|`
  *     method.
  *   - They can be executed in sequence, with the second starting as soon as
  *     the first ends. This is done by the `###` method.
  *   - The execution of the second one can be conditioned by the return code
  *     (exit status) of the first, either only when it's zero, or only when it's
  *     not zero. The methods `#&&` and `#||` accomplish these tasks.
  *
  * ==Redirecting Input/Output==
  *
  * Though control of input and output can be done when executing the process,
  * there's a few methods that create a new `ProcessBuilder` with a
  * pre-configured input or output. They are `#<`, `#>` and `#>>`, and may take
  * as input either another `ProcessBuilder` (like the pipe described above), or
  * something else such as a `java.io.File` or a `java.io.InputStream`.
  * For example:
  * {{{
  * new URL("http://databinder.net/dispatch/About") #> "grep JSON" #>> new File("About_JSON") !
  * }}}
  *
  * ==Starting Processes==
  *
  * To execute all external commands associated with a `ProcessBuilder`, one
  * may use one of four groups of methods. Each of these methods have various
  * overloads and variations to enable further control over the I/O. These
  * methods are:
  *
  *   - `run`: the most general method, it returns a
  *     [[scala.sys.process.Process]] immediately, and the external command
  *     executes concurrently.
  *   - `!`: blocks until all external commands exit, and returns the exit code
  *     of the last one in the chain of execution.
  *   - `!!`: blocks until all external commands exit, and returns a `String`
  *     with the output generated.
  *   - `lineStream`: returns immediately like `run`, and the output being generated
  *     is provided through a `Stream[String]`. Getting the next element of that
  *     `Stream` may block until it becomes available. This method will throw an
  *     exception if the return code is different than zero -- if this is not
  *     desired, use the `lineStream_!` method.
  *
  * ==Handling Input and Output==
  *
  * If not specified, the input of the external commands executed with `run` or
  * `!` will not be tied to anything, and the output will be redirected to the
  * stdout and stderr of the Scala process. For the methods `!!` and `lines`, no
  * input will be provided, and the output will be directed according to the
  * semantics of these methods.
  *
  * Some methods will cause stdin to be used as input. Output can be controlled
  * with a [[scala.sys.process.ProcessLogger]] -- `!!` and `lines` will only
  * redirect error output when passed a `ProcessLogger`. If one desires full
  * control over input and output, then a [[scala.sys.process.ProcessIO]] can be
  * used with `run`.
  *
  * For example, we could silence the error output from `lines_!` like this:
  * {{{
  * val etcFiles = "find /etc" lines_! ProcessLogger(line => ())
  * }}}
  *
  * ==Extended Example==
  *
  * Let's examine in detail one example of usage:
  * {{{
  * import scala.sys.process._
  * "find src -name *.scala -exec grep null {} ;"  #|  "xargs test -z"  #&&  "echo null-free"  #||  "echo null detected"  !
  * }}}
  * Note that every `String` is implicitly converted into a `ProcessBuilder`
  * through the implicits imported from [[scala.sys.process]]. These `ProcessBuilder` are then
  * combined in three different ways.
  *
  *   1. `#|` pipes the output of the first command into the input of the second command. It
  *      mirrors a shell pipe (`|`).
  *   1. `#&&` conditionally executes the second command if the previous one finished with
  *      exit value 0. It mirrors shell's `&&`.
  *   1. `#||` conditionally executes the third command if the exit value of the previous
  *      command is different than zero. It mirrors shell's `||`.
  *
  * Finally, `!` at the end executes the commands, and returns the exit value.
  * Whatever is printed will be sent to the Scala process standard output. If
  * we wanted to capture it, we could run that with `!!` instead.
  *
  * Note: though it is not shown above, the equivalent of a shell's `;` would be
  * `###`. The reason for this name is that `;` is a reserved token in Scala.
  *
  * Note: the `lines` method, though deprecated, may conflict with the `StringLike`
  * method of the same name.  To avoid this, one may wish to call the builders in
  * `Process` instead of importing `scala.sys.process._`.  The example above would be
  * {{{
  * import scala.sys.process.Process
  * Process("find src -name *.scala -exec grep null {} ;") #| Process("xargs test -z") #&& Process("echo null-free") #|| Process("echo null detected") !
  * }}}
  */
trait ProcessBuilder extends Source with Sink {
  /** Starts the process represented by this builder, blocks until it exits, and
    * returns the output as a String.  Standard error is sent to the console.  If
    * the exit code is non-zero, an exception is thrown.
    */
  def !! : String

  /** Starts the process represented by this builder, blocks until it exits, and
    * returns the output as a String.  Standard error is sent to the provided
    * ProcessLogger.  If the exit code is non-zero, an exception is thrown.
    */
  def !!(log: ProcessLogger): String

  /** Starts the process represented by this builder, blocks until it exits, and
    * returns the output as a String.  Standard error is sent to the console.  If
    * the exit code is non-zero, an exception is thrown.  The newly started
    * process reads from standard input of the current process.
    */
  def !!< : String

  /** Starts the process represented by this builder, blocks until it exits, and
    * returns the output as a String.  Standard error is sent to the provided
    * ProcessLogger.  If the exit code is non-zero, an exception is thrown.  The
    * newly started process reads from standard input of the current process.
    */
  def !!<(log: ProcessLogger): String

  /** Starts the process represented by this builder.  The output is returned as
    * a Stream that blocks when lines are not available but the process has not
    * completed.  Standard error is sent to the console.  If the process exits
    * with a non-zero value, the Stream will provide all lines up to termination
    * and then throw an exception.
    */
  def lineStream: Stream[String]
  
  /** Deprecated (renamed). Use `lineStream` instead. */
  @deprecated("Use lineStream instead.", "2.11.0")
  def lines: Stream[String] = lineStream

  /** Starts the process represented by this builder.  The output is returned as
    * a Stream that blocks when lines are not available but the process has not
    * completed.  Standard error is sent to the provided ProcessLogger.  If the
    * process exits with a non-zero value, the Stream will provide all lines up
    * to termination and then throw an exception.
    */
  def lineStream(log: ProcessLogger): Stream[String]
  
  /** Deprecated (renamed).  Use `lineStream(log: ProcessLogger)` instead. */
  @deprecated("Use stream instead.", "2.11.0")
  def lines(log: ProcessLogger): Stream[String] = lineStream(log)

  /** Starts the process represented by this builder.  The output is returned as
    * a Stream that blocks when lines are not available but the process has not
    * completed.  Standard error is sent to the console. If the process exits
    * with a non-zero value, the Stream will provide all lines up to termination
    * but will not throw an exception.
    */
  def lineStream_! : Stream[String]
  
  /** Deprecated (renamed).  Use `lineStream_!` instead. */
  @deprecated("Use lineStream_! instead.", "2.11.0")  
  def lines_! : Stream[String] = lineStream_!

  /** Starts the process represented by this builder.  The output is returned as
    * a Stream that blocks when lines are not available but the process has not
    * completed.  Standard error is sent to the provided ProcessLogger. If the
    * process exits with a non-zero value, the Stream will provide all lines up
    * to termination but will not throw an exception.
    */
  def lineStream_!(log: ProcessLogger): Stream[String]
  
  /** Deprecated (renamed).  Use `lineStream_!(log: ProcessLogger)` instead. */
  @deprecated("Use stream_! instead.", "2.11.0")
  def lines_!(log: ProcessLogger): Stream[String] = lineStream_!(log)

  /** Starts the process represented by this builder, blocks until it exits, and
    * returns the exit code.  Standard output and error are sent to the console.
    */
  def ! : Int

  /** Starts the process represented by this builder, blocks until it exits, and
    * returns the exit code.  Standard output and error are sent to the given
    * ProcessLogger.
    */
  def !(log: ProcessLogger): Int

  /** Starts the process represented by this builder, blocks until it exits, and
    * returns the exit code.  Standard output and error are sent to the console.
    * The newly started process reads from standard input of the current process.
    */
  def !< : Int

  /** Starts the process represented by this builder, blocks until it exits, and
    * returns the exit code.  Standard output and error are sent to the given
    * ProcessLogger.  The newly started process reads from standard input of the
    * current process.
    */
  def !<(log: ProcessLogger): Int

  /** Starts the process represented by this builder.  Standard output and error
   * are sent to the console.*/
  def run(): Process

  /** Starts the process represented by this builder.  Standard output and error
    * are sent to the given ProcessLogger.
    */
  def run(log: ProcessLogger): Process

  /** Starts the process represented by this builder.  I/O is handled by the
    * given ProcessIO instance.
    */
  def run(io: ProcessIO): Process

  /** Starts the process represented by this builder.  Standard output and error
    * are sent to the console.  The newly started process reads from standard
    * input of the current process if `connectInput` is true.
    */
  def run(connectInput: Boolean): Process

  /** Starts the process represented by this builder, blocks until it exits, and
    * returns the exit code.  Standard output and error are sent to the given
    * ProcessLogger.  The newly started process reads from standard input of the
    * current process if `connectInput` is true.
    */
  def run(log: ProcessLogger, connectInput: Boolean): Process

  /** Constructs a command that runs this command first and then `other` if this
    * command succeeds.
    */
  def #&& (other: ProcessBuilder): ProcessBuilder

  /** Constructs a command that runs this command first and then `other` if this
    * command does not succeed.
    */
  def #|| (other: ProcessBuilder): ProcessBuilder

  /** Constructs a command that will run this command and pipes the output to
    * `other`.  `other` must be a simple command.
    */
  def #| (other: ProcessBuilder): ProcessBuilder

  /** Constructs a command that will run this command and then `other`.  The
    * exit code will be the exit code of `other`.
    */
  def ### (other: ProcessBuilder): ProcessBuilder


  /** True if this command can be the target of a pipe.  */
  def canPipeTo: Boolean

  /** True if this command has an exit code which should be propagated to the
    * user.  Given a pipe between A and B, if B.hasExitValue is true then the
    * exit code will be the one from B; if it is false, the one from A.  This
    * exists to prevent output redirections (implemented as pipes) from masking
    * useful process error codes.
    */
  def hasExitValue: Boolean
}

/** This object contains traits used to describe input and output sources. */
object ProcessBuilder extends ProcessBuilderImpl {
  /** Used when creating [[scala.sys.process.ProcessBuilder.Source]] from an URL. */
  trait URLBuilder extends Source {

  }

  /** Used when creating [[scala.sys.process.ProcessBuilder.Source]] and/or
    * [[scala.sys.process.ProcessBuilder.Sink]] from a file.
    */
  trait FileBuilder extends Sink with Source {
    /** Append the contents of a `java.io.File` to this file */
    def #<<(f: File): ProcessBuilder

    /** Append the contents from a `java.net.URL` to this file */
    def #<<(u: URL): ProcessBuilder

    /** Append the contents of a `java.io.InputStream` to this file */
    def #<<(i: => InputStream): ProcessBuilder

    /** Append the contents of a [[scala.sys.process.ProcessBuilder]] to this file */
    def #<<(p: ProcessBuilder): ProcessBuilder
  }

  /** Represents everything that can be used as an input to a
    * [[scala.sys.process.ProcessBuilder]].
    */
  trait Source {
    protected def toSource: ProcessBuilder

    /** Writes the output stream of this process to the given file. */
    def #> (f: File): ProcessBuilder = toFile(f, append = false)

    /** Appends the output stream of this process to the given file. */
    def #>> (f: File): ProcessBuilder = toFile(f, append = true)

    /** Writes the output stream of this process to the given OutputStream. The
      * argument is call-by-name, so the stream is recreated, written, and closed each
      * time this process is executed.
      */
    def #>(out: => OutputStream): ProcessBuilder = #> (new OStreamBuilder(out, "<output stream>"))

    /** Writes the output stream of this process to a [[scala.sys.process.ProcessBuilder]]. */
    def #>(b: ProcessBuilder): ProcessBuilder = new PipedBuilder(toSource, b, false)

    /** Returnes a [[scala.sys.process.ProcessBuilder]] representing this `Source`. */
    def cat = toSource
    private def toFile(f: File, append: Boolean) = #> (new FileOutput(f, append))
  }

  /** Represents everything that can receive an output from a
    * [[scala.sys.process.ProcessBuilder]].
    */
  trait Sink {
    protected def toSink: ProcessBuilder

    /** Reads the given file into the input stream of this process. */
    def #< (f: File): ProcessBuilder = #< (new FileInput(f))

    /** Reads the given URL into the input stream of this process. */
    def #< (f: URL): ProcessBuilder = #< (new URLInput(f))

    /** Reads the given InputStream into the input stream of this process. The
      * argument is call-by-name, so the stream is recreated, read, and closed each
      * time this process is executed.
      */
    def #<(in: => InputStream): ProcessBuilder = #< (new IStreamBuilder(in, "<input stream>"))

    /** Reads the output of a [[scala.sys.process.ProcessBuilder]] into the input stream of this process. */
    def #<(b: ProcessBuilder): ProcessBuilder = new PipedBuilder(b, toSink, false)
  }
}