Scala Standard Library2.12.4 < Back

Packages

package root
This is the documentation for the Scala standard library.
This is the documentation for the Scala standard library.
Package structure
The scala package contains core types like Int, Float, Array or Option which are accessible in all Scala compilation units without explicit qualification or imports.
Notable packages include:
- scala.collection and its sub-packages contain Scala's collections framework
  - scala.collection.immutable - Immutable, sequential data-structures such as Vector, List, Range, HashMap or HashSet
  - scala.collection.mutable - Mutable, sequential data-structures such as ArrayBuffer, StringBuilder, HashMap or HashSet
  - scala.collection.concurrent - Mutable, concurrent data-structures such as TrieMap
  - scala.collection.parallel.immutable - Immutable, parallel data-structures such as ParVector, ParRange, ParHashMap or ParHashSet
  - scala.collection.parallel.mutable - Mutable, parallel data-structures such as ParArray, ParHashMap, ParTrieMap or ParHashSet
- scala.concurrent - Primitives for concurrent programming such as Futures and Promises
- scala.io - Input and output operations
- scala.math - Basic math functions and additional numeric types like BigInt and BigDecimal
- scala.sys - Interaction with other processes and the operating system
- scala.util.matching - Regular expressions
Other packages exist. See the complete list on the right.
Additional parts of the standard library are shipped as separate libraries. These include:
- scala.reflect - Scala's reflection API (scala-reflect.jar)
- scala.xml - XML parsing, manipulation, and serialization (scala-xml.jar)
- scala.swing - A convenient wrapper around Java's GUI framework called Swing (scala-swing.jar)
- scala.util.parsing - Parser combinators (scala-parser-combinators.jar)
Automatic imports
Identifiers in the scala package and the scala.Predef object are always in scope by default.
Some of these identifiers are type aliases provided as shortcuts to commonly used classes. For example, List is an alias for scala.collection.immutable.List.
Other aliases refer to classes provided by the underlying platform. For example, on the JVM, String is an alias for java.lang.String.
Definition Classes
root
package scala
Core Scala types.
Core Scala types. They are always available without an explicit import.

Definition Classes
root
package sys
The package object scala.sys contains methods for reading and altering core aspects of the virtual machine as well as the world outside of it.
The package object scala.sys contains methods for reading and altering core aspects of the virtual machine as well as the world outside of it.

Definition Classes
scala
Version
2.9
Since
2.9
package process
This package handles the execution of external processes.
This package handles the execution of external processes. The contents of this package can be divided in three groups, according to their responsibilities:
- Indicating what to run and how to run it.
- Handling a process input and output.
- Running the process.
For simple uses, the only group that matters is the first one. Running an external command can be as simple as "ls".!, or as complex as building a pipeline of commands such as this:
```
import scala.sys.process._
"ls" #| "grep .scala" #&& Seq("sh", "-c", "scalac *.scala") #|| "echo nothing found" lineStream
```
We describe below the general concepts and architecture of the package, and then take a closer look at each of the categories mentioned above.
Concepts and Architecture
The underlying basis for the whole package is Java's Process and ProcessBuilder classes. While there's no need to use these Java classes, they impose boundaries on what is possible. One cannot, for instance, retrieve a process id for whatever is executing.
When executing an external process, one can provide a command's name, arguments to it, the directory in which it will be executed and what environment variables will be set. For each executing process, one can feed its standard input through a java.io.OutputStream, and read from its standard output and standard error through a pair of java.io.InputStream. One can wait until a process finishes execution and then retrieve its return value, or one can kill an executing process. Everything else must be built on those features.
This package provides a DSL for running and chaining such processes, mimicking Unix shells ability to pipe output from one process to the input of another, or control the execution of further processes based on the return status of the previous one.
In addition to this DSL, this package also provides a few ways of controlling input and output of these processes, going from simple and easy to use to complex and flexible.
When processes are composed, a new ProcessBuilder is created which, when run, will execute the ProcessBuilder instances it is composed of according to the manner of the composition. If piping one process to another, they'll be executed simultaneously, and each will be passed a ProcessIO that will copy the output of one to the input of the other.
What to Run and How
The central component of the process execution DSL is the scala.sys.process.ProcessBuilder trait. It is ProcessBuilder that implements the process execution DSL, that creates the scala.sys.process.Process that will handle the execution, and return the results of such execution to the caller. We can see that DSL in the introductory example: #|, #&& and #!! are methods on ProcessBuilder used to create a new ProcessBuilder through composition.
One creates a ProcessBuilder either through factories on the scala.sys.process.Process's companion object, or through implicit conversions available in this package object itself. Implicitly, each process is created either out of a String, with arguments separated by spaces -- no escaping of spaces is possible -- or out of a scala.collection.Seq, where the first element represents the command name, and the remaining elements are arguments to it. In this latter case, arguments may contain spaces.
To further control what how the process will be run, such as specifying the directory in which it will be run, see the factories on scala.sys.process.Process's object companion.
Once the desired ProcessBuilder is available, it can be executed in different ways, depending on how one desires to control its I/O, and what kind of result one wishes for:
- Return status of the process (! methods)
- Output of the process as a String (!! methods)
- Continuous output of the process as a Stream[String] (lineStream methods)
- The Process representing it (run methods)
Some simple examples of these methods:
```
import scala.sys.process._

// This uses ! to get the exit code
def fileExists(name: String) = Seq("test", "-f", name).! == 0

// This uses !! to get the whole result as a string
val dirContents = "ls".!!

// This "fire-and-forgets" the method, which can be lazily read through
// a Stream[String]
def sourceFilesAt(baseDir: String): Stream[String] = {
  val cmd = Seq("find", baseDir, "-name", "*.scala", "-type", "f")
  cmd.lineStream
}
```
We'll see more details about controlling I/O of the process in the next section.
Handling Input and Output
In the underlying Java model, once a Process has been started, one can get java.io.InputStream and java.io.OutputStream representing its output and input respectively. That is, what one writes to an OutputStream is turned into input to the process, and the output of a process can be read from an InputStream -- of which there are two, one representing normal output, and the other representing error output.
This model creates a difficulty, which is that the code responsible for actually running the external processes is the one that has to take decisions about how to handle its I/O.
This package presents an alternative model: the I/O of a running process is controlled by a scala.sys.process.ProcessIO object, which can be passed _to_ the code that runs the external process. A ProcessIO will have direct access to the java streams associated with the process I/O. It must, however, close these streams afterwards.
Simpler abstractions are available, however. The components of this package that handle I/O are:
- scala.sys.process.ProcessIO: provides the low level abstraction.
- scala.sys.process.ProcessLogger: provides a higher level abstraction for output, and can be created through its object companion
- scala.sys.process.BasicIO: a library of helper methods for the creation of ProcessIO.
- This package object itself, with a few implicit conversions.
Some examples of I/O handling:
```
import scala.sys.process._

// An overly complex way of computing size of a compressed file
def gzFileSize(name: String) = {
  val cat = Seq("zcat", name)
  var count = 0
  def byteCounter(input: java.io.InputStream) = {
    while(input.read() != -1) count += 1
    input.close()
  }
  val p = cat run new ProcessIO(_.close(), byteCounter, _.close())
  p.exitValue()
  count
}

// This "fire-and-forgets" the method, which can be lazily read through
// a Stream[String], and accumulates all errors on a StringBuffer
def sourceFilesAt(baseDir: String): (Stream[String], StringBuffer) = {
  val buffer = new StringBuffer()
  val cmd = Seq("find", baseDir, "-name", "*.scala", "-type", "f")
  val lineStream = cmd lineStream_! ProcessLogger(buffer append _)
  (lineStream, buffer)
}
```
Instances of the java classes java.io.File and java.net.URL can both be used directly as input to other processes, and java.io.File can be used as output as well. One can even pipe one to the other directly without any intervening process, though that's not a design goal or recommended usage. For example, the following code will copy a web page to a file:
```
import java.io.File
import java.net.URL
import scala.sys.process._
new URL("http://www.scala-lang.org/") #> new File("scala-lang.html") !
```
More information about the other ways of controlling I/O can be found in the Scaladoc for the associated objects, traits and classes.
Running the Process
Paradoxically, this is the simplest component of all, and the one least likely to be interacted with. It consists solely of scala.sys.process.Process, and it provides only two methods:
- exitValue(): blocks until the process exit, and then returns the exit value. This is what happens when one uses the ! method of ProcessBuilder.
- destroy(): this will kill the external process and close the streams associated with it.
Definition Classes
sys
BasicIO
FileProcessLogger
Process
ProcessBuilder
ProcessCreation
ProcessIO
ProcessImplicits
ProcessLogger

scala.sys.process

ProcessIO

final class ProcessIO extends AnyRef

This class is used to control the I/O of every scala.sys.process.Process. The functions used to create it will be called with the process streams once it has been started. It might not be necessary to use ProcessIO directly -- scala.sys.process.ProcessBuilder can return the process output to the caller, or use a scala.sys.process.ProcessLogger which avoids direct interaction with a stream. One can even use the factories at BasicIO to create a ProcessIO, or use its helper methods when creating one's own ProcessIO.

When creating a ProcessIO, it is important to close all streams when finished, since the JVM might use system resources to capture the process input and output, and will not release them unless the streams are explicitly closed.

ProcessBuilder will call writeInput, processOutput and processError in separate threads, and if daemonizeThreads is true, they will all be marked as daemon threads.

Source: ProcessIO.scala
Note: Failure to close the passed streams may result in resource leakage.

Linear Supertypes

AnyRef, Any

Type Hierarchy

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Inherited

ProcessIO
AnyRef
Any

Implicitly

by any2stringadd
by StringFormat
by Ensuring
by ArrowAssoc

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Visibility

Public
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Instance Constructors

new ProcessIO(in: (OutputStream) ⇒ Unit, out: (InputStream) ⇒ Unit, err: (InputStream) ⇒ Unit)
new ProcessIO(writeInput: (OutputStream) ⇒ Unit, processOutput: (InputStream) ⇒ Unit, processError: (InputStream) ⇒ Unit, daemonizeThreads: Boolean)
writeInput
Function that will be called with the OutputStream to which all input to the process must be written. This will be called in a newly spawned thread.
processOutput
Function that will be called with the InputStream from which all normal output of the process must be read from. This will be called in a newly spawned thread.
processError
Function that will be called with the InputStream from which all error output of the process must be read from. This will be called in a newly spawned thread.
daemonizeThreads
Indicates whether the newly spawned threads that will run processOutput, processError and writeInput should be marked as daemon threads.

Value Members

final def !=(arg0: Any): Boolean
Test two objects for inequality.
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.
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 +(other: String): String

Implicit
This member is added by an implicit conversion from ProcessIO to any2stringadd[ProcessIO] performed by method any2stringadd in scala.Predef.
Definition Classes
any2stringadd
def ->[B](y: B): (ProcessIO, B)

Implicit
This member is added by an implicit conversion from ProcessIO to ArrowAssoc[ProcessIO] 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).
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.
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 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[java.lang]
Definition Classes
AnyRef
Annotations
@native() @throws( ... )
Note
not specified by SLS as a member of AnyRef
val daemonizeThreads: Boolean
def daemonized(): ProcessIO
Creates a new ProcessIO, with daemonizeThreads true.
def ensuring(cond: (ProcessIO) ⇒ Boolean, msg: ⇒ Any): ProcessIO

Implicit
This member is added by an implicit conversion from ProcessIO to Ensuring[ProcessIO] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
def ensuring(cond: (ProcessIO) ⇒ Boolean): ProcessIO

Implicit
This member is added by an implicit conversion from ProcessIO to Ensuring[ProcessIO] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
def ensuring(cond: Boolean, msg: ⇒ Any): ProcessIO

Implicit
This member is added by an implicit conversion from ProcessIO to Ensuring[ProcessIO] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
def ensuring(cond: Boolean): ProcessIO

Implicit
This member is added by an implicit conversion from ProcessIO to Ensuring[ProcessIO] 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).
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.
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.
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[java.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.
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 ProcessIO to StringFormat[ProcessIO] 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 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.
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.
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).
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.
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.
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
val processError: (InputStream) ⇒ Unit
val processOutput: (InputStream) ⇒ Unit
final def synchronized[T0](arg0: ⇒ T0): T0

Definition Classes
AnyRef
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
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
@native() @throws( ... )
def withError(process: (InputStream) ⇒ Unit): ProcessIO
Creates a new ProcessIO with a different handler for the error output.
def withInput(write: (OutputStream) ⇒ Unit): ProcessIO
Creates a new ProcessIO with a different handler for the process input.
def withOutput(process: (InputStream) ⇒ Unit): ProcessIO
Creates a new ProcessIO with a different handler for the normal output.
val writeInput: (OutputStream) ⇒ Unit
def →[B](y: B): (ProcessIO, B)

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

Packages

Package structure

Automatic imports

Concepts and Architecture

What to Run and How

Handling Input and Output

Running the Process

ProcessIO

final class ProcessIO extends AnyRef

Instance Constructors

Value Members

Inherited from AnyRef

Inherited from Any

Inherited by implicit conversion any2stringadd from ProcessIO to any2stringadd[ProcessIO]

Inherited by implicit conversion StringFormat from ProcessIO to StringFormat[ProcessIO]

Inherited by implicit conversion Ensuring from ProcessIO to Ensuring[ProcessIO]

Inherited by implicit conversion ArrowAssoc from ProcessIO to ArrowAssoc[ProcessIO]

Ungrouped

Packages

Package structure

Automatic imports

Concepts and Architecture

What to Run and How

Handling Input and Output

Running the Process

ProcessIO 

final class ProcessIO extends AnyRef

Instance Constructors

Value Members

Inherited from AnyRef

Inherited from Any

Inherited by implicit conversion any2stringadd from ProcessIO to any2stringadd[ProcessIO]

Inherited by implicit conversion StringFormat from ProcessIO to StringFormat[ProcessIO]

Inherited by implicit conversion Ensuring from ProcessIO to Ensuring[ProcessIO]

Inherited by implicit conversion ArrowAssoc from ProcessIO to ArrowAssoc[ProcessIO]

Ungrouped

ProcessIO