trait ProcessBuilder extends Source with Sink
Represents a sequence of one or more external processes that can be
executed. A ProcessBuilder
can be a single external process, or a
combination of other ProcessBuilder
. 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 a ProcessBuilder
through factories provided in
scala.sys.process.Process's companion object, or implicit conversions
based on these factories made available in the package object
scala.sys.process. Here are some examples:
import scala.sys.process._ // Executes "ls" and sends output to stdout "ls".! // Execute "ls" and assign a `Stream[String]` of its output to "contents". val contents = Process("ls").lineStream // Here we use a `Seq` to make the parameter whitespace-safe def contentsOf(dir: String): String = Seq("ls", dir).!!
The methods of ProcessBuilder
are divided in three categories: the ones that
combine two ProcessBuilder
to create a third, the ones that redirect input
or output of a ProcessBuilder
, and the ones that execute
the external processes associated with it.
Combining ProcessBuilder
Two existing ProcessBuilder
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 new ProcessBuilder
with a
pre-configured input or output. They are #<
, #>
and #>>
, and may take
as input either another ProcessBuilder
(like the pipe described above), or
something else such as a java.io.File
or a java.io.InputStream
.
For example:
new URL("http://databinder.net/dispatch/About") #> "grep JSON" #>> new File("About_JSON") !
Starting Processes
To execute all external commands associated with a ProcessBuilder
, 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 a scala.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.lineStream
: returns immediately likerun
, and the output being generated is provided through aStream[String]
. Getting the next element of thatStream
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 thelineStream_!
method.
Handling Input and Output
If not specified, the input of the external commands executed with run
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 !!
and lineStream
, 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 a scala.sys.process.ProcessLogger -- !!
and lineStream
will only
redirect error output when passed a ProcessLogger
. If one desires full
control over input and output, then a scala.sys.process.ProcessIO can be
used with run
.
For example, we could silence the error output from lineStream_!
like this:
val etcFiles = "find /etc" lineStream_! 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 every String
is implicitly converted into a ProcessBuilder
through the implicits imported from scala.sys.process. These ProcessBuilder
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.
Note: the lines
method, though deprecated, may conflict with the StringLike
method of the same name. To avoid this, one may wish to call the builders in
Process
instead of importing scala.sys.process._
. The example above would be
import scala.sys.process.Process Process("find src -name *.scala -exec grep null {} ;") #| Process("xargs test -z") #&& Process("echo null-free") #|| Process("echo null detected") !
- Source
- ProcessBuilder.scala
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- By Inheritance
- ProcessBuilder
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Abstract Value Members
-
abstract
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.
-
abstract
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.
-
abstract
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.
-
abstract
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.
-
abstract
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. The newly started process reads from standard input of the current process.
-
abstract
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.
-
abstract
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.
-
abstract
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.
-
abstract
def
###(other: ProcessBuilder): ProcessBuilder
Constructs a command that will run this command and then
other
.Constructs a command that will run this command and then
other
. The exit code will be the exit code ofother
. -
abstract
def
#&&(other: ProcessBuilder): ProcessBuilder
Constructs a command that runs this command first and then
other
if this command succeeds. -
abstract
def
#|(other: ProcessBuilder): ProcessBuilder
Constructs a command that will run this command and pipes the output to
other
.Constructs a command that will run this command and pipes the output to
other
.other
must be a simple command. -
abstract
def
#||(other: ProcessBuilder): ProcessBuilder
Constructs a command that runs this command first and then
other
if this command does not succeed. -
abstract
def
canPipeTo: Boolean
True if this command can be the target of a pipe.
-
abstract
def
hasExitValue: 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.
-
abstract
def
lineStream(log: ProcessLogger): Stream[String]
Starts the process represented by this builder.
Starts the process represented by this builder. The output is returned as a Stream that blocks when lines are not available but the process has not completed. Standard error is sent to the provided ProcessLogger. If the process exits with a non-zero value, the Stream will provide all lines up to termination and then throw an exception.
-
abstract
def
lineStream: Stream[String]
Starts the process represented by this builder.
Starts the process represented by this builder. The output is returned as a Stream that blocks when lines are not available but the process has not completed. Standard error is sent to the console. If the process exits with a non-zero value, the Stream will provide all lines up to termination and then throw an exception.
-
abstract
def
lineStream_!(log: ProcessLogger): Stream[String]
Starts the process represented by this builder.
Starts the process represented by this builder. The output is returned as a Stream that blocks when lines are not available but the process has not completed. Standard error is sent to the provided ProcessLogger. If the process exits with a non-zero value, the Stream will provide all lines up to termination but will not throw an exception.
-
abstract
def
lineStream_!: Stream[String]
Starts the process represented by this builder.
Starts the process represented by this builder. The output is returned as a Stream that blocks when lines are not available but the process has not completed. Standard error is sent to the console. If the process exits with a non-zero value, the Stream will provide all lines up to termination but will not throw an exception.
-
abstract
def
run(log: ProcessLogger, connectInput: Boolean): Process
Starts the process represented by this builder.
Starts the process represented by this builder. Standard output and error are sent to the given ProcessLogger. The newly started process reads from standard input of the current process if
connectInput
is true. -
abstract
def
run(connectInput: Boolean): Process
Starts the process represented by this builder.
Starts the process represented by this builder. Standard output and error are sent to the console. The newly started process reads from standard input of the current process if
connectInput
is true. -
abstract
def
run(io: ProcessIO): Process
Starts the process represented by this builder.
Starts the process represented by this builder. I/O is handled by the given ProcessIO instance.
-
abstract
def
run(log: ProcessLogger): Process
Starts the process represented by this builder.
Starts the process represented by this builder. Standard output and error are sent to the given ProcessLogger.
-
abstract
def
run(): Process
Starts the process represented by this builder.
Starts the process represented by this builder. Standard output and error are sent to the console.
Concrete Value Members
-
def
#<(b: ProcessBuilder): ProcessBuilder
Reads the output of a scala.sys.process.ProcessBuilder into the input stream of this process.
Reads the output of a scala.sys.process.ProcessBuilder into the input stream of this process.
- Definition Classes
- Sink
-
def
#<(in: ⇒ InputStream): ProcessBuilder
Reads the given InputStream into the input stream of this process.
Reads the given InputStream into the input stream of this process. The argument is call-by-name, so the stream is recreated, read, and closed each time this process is executed.
- Definition Classes
- Sink
-
def
#<(f: URL): ProcessBuilder
Reads the given URL into the input stream of this process.
Reads the given URL into the input stream of this process.
- Definition Classes
- Sink
-
def
#<(f: File): ProcessBuilder
Reads the given file into the input stream of this process.
Reads the given file into the input stream of this process.
- Definition Classes
- Sink
-
def
#>(b: ProcessBuilder): ProcessBuilder
Writes the output stream of this process to a scala.sys.process.ProcessBuilder.
Writes the output stream of this process to a scala.sys.process.ProcessBuilder.
- Definition Classes
- Source
-
def
#>(out: ⇒ OutputStream): ProcessBuilder
Writes the output stream of this process to the given OutputStream.
Writes the output stream of this process to the given OutputStream. The argument is call-by-name, so the stream is recreated, written, and closed each time this process is executed.
- Definition Classes
- Source
-
def
#>(f: File): ProcessBuilder
Writes the output stream of this process to the given file.
Writes the output stream of this process to the given file.
- Definition Classes
- Source
-
def
#>>(f: File): ProcessBuilder
Appends the output stream of this process to the given file.
Appends the output stream of this process to the given file.
- Definition Classes
- Source
-
def
cat: ProcessBuilder
Returns a scala.sys.process.ProcessBuilder representing this
Source
.Returns a scala.sys.process.ProcessBuilder representing this
Source
.- Definition Classes
- Source
Deprecated Value Members
-
def
lines(log: ProcessLogger): Stream[String]
Deprecated (renamed).
Deprecated (renamed). Use
lineStream(log: ProcessLogger)
instead.- Annotations
- @deprecated
- Deprecated
(Since version 2.11.0) use lineStream instead
-
def
lines: Stream[String]
Deprecated (renamed).
Deprecated (renamed). Use
lineStream
instead.- Annotations
- @deprecated
- Deprecated
(Since version 2.11.0) use lineStream instead
-
def
lines_!(log: ProcessLogger): Stream[String]
Deprecated (renamed).
Deprecated (renamed). Use
lineStream_!(log: ProcessLogger)
instead.- Annotations
- @deprecated
- Deprecated
(Since version 2.11.0) use lineStream_! instead
-
def
lines_!: Stream[String]
Deprecated (renamed).
Deprecated (renamed). Use
lineStream_!
instead.- Annotations
- @deprecated
- Deprecated
(Since version 2.11.0) use lineStream_! instead
This is the documentation for the Scala standard library.
Package structure
The scala package contains core types like
Int
,Float
,Array
orOption
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 frameworkscala.collection.immutable
- Immutable, sequential data-structures such asVector
,List
,Range
,HashMap
orHashSet
scala.collection.mutable
- Mutable, sequential data-structures such asArrayBuffer
,StringBuilder
,HashMap
orHashSet
scala.collection.concurrent
- Mutable, concurrent data-structures such asTrieMap
scala.collection.parallel.immutable
- Immutable, parallel data-structures such asParVector
,ParRange
,ParHashMap
orParHashSet
scala.collection.parallel.mutable
- Mutable, parallel data-structures such asParArray
,ParHashMap
,ParTrieMap
orParHashSet
scala.concurrent
- Primitives for concurrent programming such asFutures
andPromises
scala.io
- Input and output operationsscala.math
- Basic math functions and additional numeric types likeBigInt
andBigDecimal
scala.sys
- Interaction with other processes and the operating systemscala.util.matching
- Regular expressionsOther 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 forscala.collection.immutable.List
.Other aliases refer to classes provided by the underlying platform. For example, on the JVM,
String
is an alias forjava.lang.String
.