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ProcessBuilder

scala.sys.process.ProcessBuilder

See theProcessBuilder companion object

traitProcessBuilder extendsSource,Sink

Represents a sequence of one or more external processes that can be executed. AProcessBuilder can be a single external process, or a combination of otherProcessBuilder. 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 aProcessBuilder through factories provided inscala.sys.process.Process's companion object, or implicit conversions based on these factories made available in the package objectscala.sys.process. Here are some examples:

import scala.sys.process._// Executes "ls" and sends output to stdout"ls".!// Execute "ls" and assign a `LazyList[String]` of its output to "contents".val contents = Process("ls").lazyLines// Here we use a `Seq` to make the parameter whitespace-safedef contentsOf(dir: String): String = Seq("ls", dir).!!

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

Combining`ProcessBuilder`

Two existingProcessBuilder 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 newProcessBuilder with a pre-configured input or output. They are#<,#> and#>>, and may take as input either anotherProcessBuilder (like the pipe described above), or something else such as ajava.io.File or ajava.io.InputStream. For example:

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

Starting Processes

To execute all external commands associated with aProcessBuilder, 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 ascala.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 aString with the output generated.
lazyLines: returns immediately likerun, and the output being generated is provided through aLazyList[String]. Getting the next element of thatLazyList 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 thelazyLines_! method.

Handling Input and Output

If not specified, the input of the external commands executed withrun 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!! andlazyLines, 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 ascala.sys.process.ProcessLogger --!! andlazyLines will only redirect error output when passed aProcessLogger. If one desires full control over input and output, then ascala.sys.process.ProcessIO can be used withrun.

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

val etcFiles = "find /etc" lazyLines_! 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 everyString is implicitly converted into aProcessBuilder through the implicits imported fromscala.sys.process. TheseProcessBuilder are then combined in three different ways.

#| pipes the output of the first command into the input of the second command. It mirrors a shell pipe (|).
#&& conditionally executes the second command if the previous one finished with exit value 0. It mirrors shell's&&.
#|| 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.

Attributes

Companion: object
Source: ProcessBuilder.scala
Graph
Supertypes: traitSink
traitSource
classObject
traitMatchable
classAny

Members list

Value members

Abstract methods

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.

Attributes

Source: ProcessBuilder.scala

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.

Attributes

Source: ProcessBuilder.scala

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.

Attributes

Source: ProcessBuilder.scala

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.

Attributes

Source: ProcessBuilder.scala

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

Attributes

Source: ProcessBuilder.scala

def!!<(log:ProcessLogger):String

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

Attributes

Source: ProcessBuilder.scala

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.

Attributes

Source: ProcessBuilder.scala

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.

Attributes

Source: ProcessBuilder.scala

def###(other:ProcessBuilder):ProcessBuilder

Constructs a command that will run this command and thenother.

Constructs a command that will run this command and thenother. The exit code will be the exit code ofother.

Attributes

Source: ProcessBuilder.scala

def#&&(other:ProcessBuilder):ProcessBuilder

Constructs a command that runs this command first and thenother if this command succeeds.

Attributes

Source: ProcessBuilder.scala

def#|(other:ProcessBuilder):ProcessBuilder

Constructs a command that will run this command and pipes the output toother.

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

Attributes

Source: ProcessBuilder.scala

def#||(other:ProcessBuilder):ProcessBuilder

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

Attributes

Source: ProcessBuilder.scala

defcanPipeTo:Boolean

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

Attributes

Source: ProcessBuilder.scala

defhasExitValue: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.