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/*
* Scala (https://www.scala-lang.org)
*
* Copyright EPFL and Lightbend, Inc.
*
* Licensed under Apache License 2.0
* (http://www.apache.org/licenses/LICENSE-2.0).
*
* See the NOTICE file distributed with this work for
* additional information regarding copyright ownership.
*/
// Developer note:
// scala -J-Dscala.process.debug
// for process debugging output.
//
package scala.sys {
/** 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" lazyLines
* }}}
*
* 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 companion object.
*
* 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 `LazyList[String]` (`lazyLines` 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 LazyList[String]
* def sourceFilesAt(baseDir: String): LazyList[String] = {
* val cmd = Seq("find", baseDir, "-name", "*.scala", "-type", "f")
* cmd.lazyLines
* }
* }}}
*
* 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 companion object.
* - [[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 LazyList[String], and accumulates all errors on a StringBuffer
* def sourceFilesAt(baseDir: String): (LazyList[String], StringBuffer) = {
* val buffer = new StringBuffer()
* val cmd = Seq("find", baseDir, "-name", "*.scala", "-type", "f")
* val lazyLines = cmd lazyLines_! ProcessLogger(buffer append _)
* (lazyLines, 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("https://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.
*/
package object process extends ProcessImplicits {
/** The input stream of this process */
def stdin = java.lang.System.in
/** The output stream of this process */
def stdout = java.lang.System.out
/** The error stream of this process */
def stderr = java.lang.System.err
}
// private val shell: String => Array[String] =
// if (isWin) Array("cmd.exe", "/C", _)
// else Array("sh", "-c", _)
package process {
// These are in a nested object instead of at the package level
// due to the issues described in tickets #3160 and #3836.
private[process] object processInternal {
final val processDebug = props contains "scala.process.debug"
dbg("Initializing process package.")
type =?>[-A, +B] = PartialFunction[A, B]
type Closeable = java.io.Closeable
type File = java.io.File
type IOException = java.io.IOException
type InterruptedIOException = java.io.InterruptedIOException
type InputStream = java.io.InputStream
type JProcess = java.lang.Process
type JProcessBuilder = java.lang.ProcessBuilder
type OutputStream = java.io.OutputStream
type URL = java.net.URL
@deprecated("Use `java.util.concurrent.LinkedBlockingQueue with capacity 1` instead.", since = "2.13.4")
type SyncVar[T] = scala.concurrent.SyncVar[T]
def onError[T](handler: Throwable => T): Throwable =?> T = {
case e @ _ => handler(e)
}
def onIOInterrupt[T](handler: => T): Throwable =?> T = {
case _: InterruptedIOException => handler
}
def onInterrupt[T](handler: => T): Throwable =?> T = {
case _: InterruptedException => handler
}
def ioFailure[T](handler: IOException => T): Throwable =?> T = {
case e: IOException => handler(e)
}
def dbg(msgs: Any*) = if (processDebug) {
Console.println("[process] " + (msgs mkString " "))
}
}
}
}
