Scala example source code file (ProcessBuilder.scala)

This example Scala source code file (ProcessBuilder.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

boolean, file, int, process, processbuilder, processlogger, source, stream, string, use

The ProcessBuilder.scala Scala example source code

/*                     __                                               *\
**     ________ ___   / /  ___     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)
  }
}