sys
A few additional conveniences for Boolean properties.
A lightweight interface wrapping a property contained in some unspecified map.
A lightweight interface wrapping a property contained in some unspecified map. Generally it'll be the system properties but this is not a requirement.
See scala.sys.SystemProperties for an example usage.
2.9
2.9
A minimal Thread wrapper to enhance shutdown hooks.
A minimal Thread wrapper to enhance shutdown hooks. It knows how to unregister itself.
2.9
2.9
A bidirectional map wrapping the java System properties.
A bidirectional map wrapping the java System properties. Changes to System properties will be immediately visible in the map, and modifications made to the map will be immediately applied to the System properties. If a security manager is in place which prevents the properties from being read or written, the AccessControlException will be caught and discarded.
The values in SystemProperties can be used to access and manipulate designated system properties.
The values in SystemProperties can be used to access and manipulate
designated system properties. See scala.sys.Prop for particulars.
if (!headless.isSet) headless.enable()
Register a shutdown hook to be run when the VM exits.
Register a shutdown hook to be run when the VM exits. The hook is automatically registered: the returned value can be ignored, but is available in case the Thread requires further modification. It can also be unregistered by calling ShutdownHookThread#remove().
Note that shutdown hooks are NOT guaranteed to be run.
the body of code to run at shutdown
the Thread which will run the shutdown hook.
Returns all active thread in the current thread's thread group and subgroups.
Returns all active thread in the current thread's thread group and subgroups.
an IndexedSeq containing the threads.
An immutable Map representing the current system environment.
An immutable Map representing the current system environment.
a Map containing the system environment variables.
Throw a new RuntimeException with the supplied message.
Throw a new RuntimeException with the supplied message.
Nothing.
Exit the JVM with the given status code.
Exit the JVM with the given status code.
Nothing.
Exit the JVM with the default status code.
Exit the JVM with the default status code.
Nothing.
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:
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" lines
We describe below the general concepts and architecture of the package, and then take a closer look at each of the categories mentioned above.
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.
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:
! methods)String (!! methods)Stream[String] (lines methods)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.lines }
We'll see more details about controlling I/O of the process in the next section.
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:
ProcessIO.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() } cat ! new ProcessIO(_.close(), byteCounter, _.close()) 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 lines = cmd lines_! ProcessLogger(buffer append _) (lines, 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 looked at in the scaladoc for the associated objects, traits and classes.
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.
A bidirectional, mutable Map representing the current system Properties.
A bidirectional, mutable Map representing the current system Properties.
a SystemProperties.
A convenience method to get the current Runtime instance.
A convenience method to get the current Runtime instance.
the result of java.lang.Runtime.getRuntime()
The package object
scala.syscontains methods for reading and altering core aspects of the virtual machine as well as the world outside of it.2.9
2.9