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 Process's companion object, or implicit conversions based on these factories made available in the package object 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".
    // Because [[scala.Predef]] already defines a `lines` method for `String`,
    // we use [[scala.sys.process.Process]]'s object companion to create it.
    val contents = Process("ls").lines

    // 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.lang.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 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. * `lines`: returns immediately like `run`, and the output being generared 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 `lines_!` 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 ProcessLogger -- `!!` and `lines` will only redirect error output when passed a `ProcessLogger`. If one desires full control over input and output, then a 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 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 caputre 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.

Source
  ProcessBuilder.scala

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1. ProcessBuilder
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### Abstract Value Members

1. #### abstract def !(log: ProcessLogger): Int

   Starts the process represented by this builder, blocks until it exits, and returns the exit code.

   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.

2. #### abstract def !: Int

   Starts the process represented by this builder, blocks until it exits, and returns the exit code.

   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.

3. #### abstract def !!(log: ProcessLogger): String

   Starts the process represented by this builder, blocks until it exits, and returns the output as a 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.

4. #### abstract def !!: String

   Starts the process represented by this builder, blocks until it exits, and returns the output as a 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.

5. #### abstract def !<(log: ProcessLogger): Int

   Starts the process represented by this builder, blocks until it exits, and returns the exit code.

   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.

6. #### abstract def !<: Int

   Starts the process represented by this builder, blocks until it exits, and returns the exit code.

   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.

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

   Constructs a command that will run this command and then `other`.

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

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

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

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

   Constructs a command that will run this command and pipes the output to `other`.

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

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

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

11. #### abstract def canPipeTo: Boolean

    True if this command can be the target of a pipe.

12. #### abstract def hasExitValue: Boolean

    True if this command has an exit code which should be propagated to the user.

    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.

13. #### abstract def lines(log: ProcessLogger): Stream[String]

    Starts the process represented by this builder.

    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.

14. #### abstract def lines: Stream[String]

    Starts the process represented by this builder.

    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.

15. #### abstract def lines_!(log: ProcessLogger): Stream[String]

    Starts the process represented by this builder.

    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.

16. #### abstract def lines_!: Stream[String]

    Starts the process represented by this builder.

    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.

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

    Starts the process represented by this builder, blocks until it exits, and returns the exit code.

    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.

18. #### abstract def run(connectInput: Boolean): Process

    Starts the process represented by this builder.

    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.

19. #### abstract def run(io: ProcessIO): Process

    Starts the process represented by this builder.

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

20. #### abstract def run(log: ProcessLogger): Process

    Starts the process represented by this builder.

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

21. #### abstract def run(): Process

    Starts the process represented by this builder.

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

22. #### abstract def toSink: ProcessBuilder

    Attributes
      protected
    Definition Classes
      Sink

23. #### abstract def toSource: ProcessBuilder

    Attributes
      protected
    Definition Classes
      Source

### Concrete Value Members

1. #### final def !=(arg0: AnyRef): Boolean

   Definition Classes
     AnyRef

2. #### final def !=(arg0: Any): Boolean

   Test two objects for inequality.

   Test two objects for inequality.

   returns

     `true` if !(this == that), false otherwise.

   Definition Classes
     Any

3. #### final def ##(): Int

   Equivalent to `x.hashCode` except for boxed numeric types.

   Equivalent to `x.hashCode` except for boxed numeric types. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them.

   returns

     a hash value consistent with ==

   Definition Classes
     AnyRef → Any

4. #### def #<(b: ProcessBuilder): ProcessBuilder

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

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

   Definition Classes
     Sink

5. #### def #<(in: ⇒ InputStream): ProcessBuilder

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

   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

6. #### def #<(f: URL): ProcessBuilder

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

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

   Definition Classes
     Sink

7. #### def #<(f: File): ProcessBuilder

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

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

   Definition Classes
     Sink

8. #### def #>(b: ProcessBuilder): ProcessBuilder

   Writes the output stream of this process to a ProcessBuilder.

   Writes the output stream of this process to a ProcessBuilder.

   Definition Classes
     Source

9. #### def #>(out: ⇒ OutputStream): ProcessBuilder

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

   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

10. #### def #>(f: File): ProcessBuilder

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

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

    Definition Classes
      Source

11. #### def #>>(f: File): ProcessBuilder

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

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

    Definition Classes
      Source

12. #### final def ==(arg0: AnyRef): Boolean

    Definition Classes
      AnyRef

13. #### final def ==(arg0: Any): Boolean

    Test two objects for equality.

    Test two objects for equality.

    returns

      `true` if the receiver object is equivalent to the argument; `false` otherwise.

    Definition Classes
      Any

14. #### final def asInstanceOf[T0]: T0

    Cast the receiver object to be of type `T0`.

    Cast the receiver object to be of type `T0`.

    Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression `1.asInstanceOf[String]` will throw a `ClassCastException` at runtime, while the expression `List(1).asInstanceOf[List[String]]` will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.

    returns

      the receiver object.

    Definition Classes
      Any
    Exceptions thrown
      ClassCastException

      if the receiver object is not an instance of the erasure of type `T0`.

15. #### def cat: ProcessBuilder

    Returnes a ProcessBuilder representing this `Source`.

    Returnes a ProcessBuilder representing this `Source`.

    Definition Classes
      Source

16. #### def clone(): AnyRef

    Create a copy of the receiver object.

    Create a copy of the receiver object.

    The default implementation of the `clone` method is platform dependent.

    returns

      a copy of the receiver object.

    Attributes
      protected[lang]
    Definition Classes
      AnyRef
    Annotations
      @throws()
    Note

      not specified by SLS as a member of AnyRef

17. #### final def eq(arg0: AnyRef): Boolean

    Tests whether the argument (`arg0`) is a reference to the receiver object (`this`).

    Tests whether the argument (`arg0`) is a reference to the receiver object (`this`).

    The `eq` method implements an equivalence relation on non-null instances of `AnyRef`, and has three additional properties:

    - It is consistent: for any non-null instances `x` and `y` of type `AnyRef`, multiple invocations of `x.eq(y)` consistently returns `true` or consistently returns `false`.
    - For any non-null instance `x` of type `AnyRef`, `x.eq(null)` and `null.eq(x)` returns `false`.
    - `null.eq(null)` returns `true`.

    When overriding the `equals` or `hashCode` methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (`o1 eq o2`), they should be equal to each other (`o1 == o2`) and they should hash to the same value (`o1.hashCode == o2.hashCode`).

    returns

      `true` if the argument is a reference to the receiver object; `false` otherwise.

    Definition Classes
      AnyRef

18. #### def equals(arg0: Any): Boolean

    The equality method for reference types.

    The equality method for reference types. See equals in Any.

    returns

      `true` if the receiver object is equivalent to the argument; `false` otherwise.

    Definition Classes
      AnyRef → Any

19. #### def finalize(): Unit

    Called by the garbage collector on the receiver object when there are no more references to the object.

    Called by the garbage collector on the receiver object when there are no more references to the object.

    The details of when and if the `finalize` method is invoked, as well as the interaction between `finalize` and non-local returns and exceptions, are all platform dependent.

    Attributes
      protected[lang]
    Definition Classes
      AnyRef
    Annotations
      @throws()
    Note

      not specified by SLS as a member of AnyRef

20. #### final def getClass(): java.lang.Class[_]

    A representation that corresponds to the dynamic class of the receiver object.

    A representation that corresponds to the dynamic class of the receiver object.

    The nature of the representation is platform dependent.

    returns

      a representation that corresponds to the dynamic class of the receiver object.

    Definition Classes
      AnyRef → Any
    Note

      not specified by SLS as a member of AnyRef

21. #### def hashCode(): Int

    The hashCode method for reference types.

    The hashCode method for reference types. See hashCode in Any.

    returns

      the hash code value for this object.

    Definition Classes
      AnyRef → Any

22. #### final def isInstanceOf[T0]: Boolean

    Test whether the dynamic type of the receiver object is `T0`.

    Test whether the dynamic type of the receiver object is `T0`.

    Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression `1.isInstanceOf[String]` will return `false`, while the expression `List(1).isInstanceOf[List[String]]` will return `true`. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the specified type.

    returns

      `true` if the receiver object is an instance of erasure of type `T0`; `false` otherwise.

    Definition Classes
      Any

23. #### final def ne(arg0: AnyRef): Boolean

    Equivalent to `!(this eq that)`.

    Equivalent to `!(this eq that)`.

    returns

      `true` if the argument is not a reference to the receiver object; `false` otherwise.

    Definition Classes
      AnyRef

24. #### final def notify(): Unit

    Wakes up a single thread that is waiting on the receiver object's monitor.

    Wakes up a single thread that is waiting on the receiver object's monitor.

    Definition Classes
      AnyRef
    Note

      not specified by SLS as a member of AnyRef

25. #### final def notifyAll(): Unit

    Wakes up all threads that are waiting on the receiver object's monitor.

    Wakes up all threads that are waiting on the receiver object's monitor.

    Definition Classes
      AnyRef
    Note

      not specified by SLS as a member of AnyRef

26. #### final def synchronized[T0](arg0: ⇒ T0): T0

    Definition Classes
      AnyRef

27. #### def toString(): String

    Creates a String representation of this object.

    Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.

    returns

      a String representation of the object.

    Definition Classes
      AnyRef → Any

28. #### final def wait(): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws()

29. #### final def wait(arg0: Long, arg1: Int): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws()

30. #### final def wait(arg0: Long): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws()

### Inherited from Sink

### Inherited from Source

### Inherited from AnyRef

### Inherited from Any