Trait 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 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 lineStream, 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 lineStream 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 lineStream_! like this:

val etcFiles = "find /etc" lineStream_! 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") !
Source
ProcessBuilder.scala
Linear Supertypes

Abstract Value Members

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.

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.

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.

abstract 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 console. If the exit code is non-zero, an exception is thrown.

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.

abstract 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 console. If the exit code is non-zero, an exception is thrown. The newly started process reads from standard input of the current process.

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.

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. The newly started process reads from standard input of the current process.

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.

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

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

abstract def canPipeTo: Boolean

abstract def hasExitValue: 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.

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.

abstract def lineStream: 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 console. If the process exits with a non-zero value, the Stream will provide all lines up to termination and then throw an exception.

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.

abstract def lineStream_!: 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 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.

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

Starts the process represented by this builder. 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.

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.

abstract def run(io: ProcessIO): Process

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

abstract def run(log: ProcessLogger): Process

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

abstract def run(): Process

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

abstract def toSink: ProcessBuilder

Attributes
protected
Definition Classes
Sink

abstract def toSource: ProcessBuilder

Attributes
protected
Definition Classes
Source

Concrete Value Members

final def !=(arg0: Any): Boolean

Test two objects for inequality.

returns

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

Definition Classes
AnyRef → Any

final def ##(): Int

Equivalent to x.hashCode except for boxed numeric types and null. 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. For null returns a hashcode where null.hashCode throws a NullPointerException.

returns

a hash value consistent with ==

Definition Classes
AnyRef → Any

def #<(b: ProcessBuilder): ProcessBuilder

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

Definition Classes
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

def #<(f: URL): ProcessBuilder

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

Definition Classes
Sink

def #<(f: File): ProcessBuilder

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

Definition Classes
Sink

def #>(b: ProcessBuilder): ProcessBuilder

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

Definition Classes
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

def #>(f: File): ProcessBuilder

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

Definition Classes
Source

def #>>(f: File): ProcessBuilder

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

Definition Classes
Source

def +(other: String): String

Implicit
This member is added by an implicit conversion from ProcessBuilder to any2stringadd[ProcessBuilder] performed by method any2stringadd in scala.Predef.
Definition Classes
any2stringadd

def ->[B](y: B): (ProcessBuilder, B)

Implicit
This member is added by an implicit conversion from ProcessBuilder to ArrowAssoc[ProcessBuilder] performed by method ArrowAssoc in scala.Predef.
Definition Classes
ArrowAssoc
Annotations
@inline()

final def ==(arg0: Any): Boolean

The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).

returns

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

Definition Classes
AnyRef → Any

final def asInstanceOf[T0]: 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.

def cat: ProcessBuilder

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

Definition Classes
Source

def clone(): AnyRef

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( ... ) @native()
Note

not specified by SLS as a member of AnyRef

def ensuring(cond: (ProcessBuilder) ⇒ Boolean, msg: ⇒ Any): ProcessBuilder

Implicit
This member is added by an implicit conversion from ProcessBuilder to Ensuring[ProcessBuilder] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring

def ensuring(cond: (ProcessBuilder) ⇒ Boolean): ProcessBuilder

Implicit
This member is added by an implicit conversion from ProcessBuilder to Ensuring[ProcessBuilder] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring

def ensuring(cond: Boolean, msg: ⇒ Any): ProcessBuilder

Implicit
This member is added by an implicit conversion from ProcessBuilder to Ensuring[ProcessBuilder] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring

def ensuring(cond: Boolean): ProcessBuilder

Implicit
This member is added by an implicit conversion from ProcessBuilder to Ensuring[ProcessBuilder] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring

final def eq(arg0: AnyRef): Boolean

Tests whether the argument (that) 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

def equals(arg0: Any): Boolean

The equality method for reference types. Default implementation delegates to eq.

See also equals in scala.Any.

returns

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

Definition Classes
AnyRef → Any

def finalize(): Unit

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( classOf[java.lang.Throwable] )
Note

not specified by SLS as a member of AnyRef

def formatted(fmtstr: String): String

Returns string formatted according to given format string. Format strings are as for String.format (@see java.lang.String.format).

Implicit
This member is added by an implicit conversion from ProcessBuilder to StringFormat[ProcessBuilder] performed by method StringFormat in scala.Predef.
Definition Classes
StringFormat
Annotations
@inline()

final def getClass(): Class[_]

Returns the runtime class representation of the object.

returns

a class object corresponding to the runtime type of the receiver.

Definition Classes
AnyRef → Any
Annotations
@native()

def hashCode(): Int

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

returns

the hash code value for this object.

Definition Classes
AnyRef → Any
Annotations
@native()

final def isInstanceOf[T0]: Boolean

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

final def ne(arg0: AnyRef): Boolean

Equivalent to !(this eq that).

returns

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

Definition Classes
AnyRef

final def notify(): Unit

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

Definition Classes
AnyRef
Annotations
@native()
Note

not specified by SLS as a member of AnyRef

final def notifyAll(): Unit

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

Definition Classes
AnyRef
Annotations
@native()
Note

not specified by SLS as a member of AnyRef

final def synchronized[T0](arg0: ⇒ T0): T0

Definition Classes
AnyRef

def toString(): String

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

final def wait(): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )

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

Definition Classes
AnyRef
Annotations
@throws( ... )

final def wait(arg0: Long): Unit

Definition Classes
AnyRef
Annotations
@throws( ... ) @native()

def →[B](y: B): (ProcessBuilder, B)

Implicit
This member is added by an implicit conversion from ProcessBuilder to ArrowAssoc[ProcessBuilder] performed by method ArrowAssoc in scala.Predef.
Definition Classes
ArrowAssoc

© 2002-2019 EPFL, with contributions from Lightbend.
Licensed under the Apache License, Version 2.0.
https://www.scala-lang.org/api/2.12.9/scala/sys/process/ProcessBuilder.html