This object contains factories forscala.sys.process.ProcessIO, which can be used to control the I/O of ascala.sys.process.Process when ascala.sys.process.ProcessBuilder is started with therun command.

It also contains some helper methods that can be used to in the creation ofProcessIO.

It is used by other classes in the package in the implementation of various features, but can also be used by client code.

Represents a process that is running or has finished running. It may be a compound process with several underlying native processes (such asa #&& b).

This trait is often not used directly, though its companion object contains factories forscala.sys.process.ProcessBuilder, the main component of this package.

It is used directly when calling the methodrun on aProcessBuilder, which makes the process run in the background. The methods provided onProcess make it possible for one to block until the process exits and get the exit value, or destroy the process altogether.

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.

CombiningProcessBuilder

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.

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.

This class is used to control the I/O of everyscala.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 useProcessIO directly --scala.sys.process.ProcessBuilder can return the process output to the caller, or use ascala.sys.process.ProcessLogger which avoids direct interaction with a stream. One can even use the factories atBasicIO to create aProcessIO, or use its helper methods when creating one's ownProcessIO.

When creating aProcessIO, it is important toclose 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 callwriteInput,processOutput andprocessError in separate threads, and if daemonizeThreads is true, they will all be marked as daemon threads.

Encapsulates the output and error streams of a running process. This is used byscala.sys.process.ProcessBuilder when starting a process, as an alternative toscala.sys.process.ProcessIO, which can be more difficult to use. Note that aProcessLogger will be used to create aProcessIO anyway. The objectBasicIO has some functions to do that.

Here is an example that counts the number of lines in the normal and error output of a process:

import scala.sys.process._var normalLines = 0var errorLines = 0val countLogger = ProcessLogger(line => normalLines += 1,                               line => errorLines += 1)"find /etc" ! countLogger

Implicitly convert ajava.io.File into ascala.sys.process.ProcessBuilder.FileBuilder, which can be used as either input or output of a process. For example:

import scala.sys.process._"ls" #> new java.io.File("dirContents.txt") !

Implicitly convert ajava.net.URL into ascala.sys.process.ProcessBuilder.URLBuilder , which can be used as input to a process. For example:

import scala.sys.process._Seq("xmllint", "--html", "-") #< new java.net.URL("https://www.scala-lang.org") #> new java.io.File("fixed.html") !