Scala Library: scala.sys.process.ProcessBuilder
scala.sys.process.ProcessBuilder
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 a 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:
```scala 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:
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 lines
, 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 lines
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 lines_!
like this:
Extended Example
Let’s examine in detail one example of usage:
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
Abstract Value Members From scala.sys.process.ProcessBuilder
abstract def !!(log: ProcessLogger): 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.
(defined at scala.sys.process.ProcessBuilder)
abstract def !!<(log: ProcessLogger): 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.
(defined at scala.sys.process.ProcessBuilder)
abstract def !(log: ProcessLogger): Int
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.
(defined at scala.sys.process.ProcessBuilder)
abstract def !<(log: ProcessLogger): Int
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.
(defined at scala.sys.process.ProcessBuilder)
abstract def lineStream(log: ProcessLogger): Stream[String]
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.
(defined at scala.sys.process.ProcessBuilder)
abstract def lineStream_!(log: ProcessLogger): Stream[String]
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.
(defined at scala.sys.process.ProcessBuilder)
abstract def run(): Process
Starts the process represented by this builder. Standard output and error are sent to the console.
(defined at scala.sys.process.ProcessBuilder)
abstract def run(connectInput: Boolean): Process
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.
(defined at scala.sys.process.ProcessBuilder)
abstract def run(io: ProcessIO): Process
Starts the process represented by this builder. I/O is handled by the given ProcessIO instance.
(defined at scala.sys.process.ProcessBuilder)
abstract def run(log: ProcessLogger): Process
Starts the process represented by this builder. Standard output and error are sent to the given ProcessLogger.
(defined at scala.sys.process.ProcessBuilder)
abstract def run(log: ProcessLogger, connectInput: Boolean): Process
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 if connectInput
is true.
(defined at scala.sys.process.ProcessBuilder)
Deprecated Value Members From scala.sys.process.ProcessBuilder
abstract def !: Int
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.
(defined at scala.sys.process.ProcessBuilder)
def lines(log: ProcessLogger): Stream[String]
Deprecated (renamed). Use lineStream(log: ProcessLogger)
instead.
- Annotations
- @ deprecated
- Deprecated
- (Since version 2.11.0) Use stream instead.
(defined at scala.sys.process.ProcessBuilder)
def lines_!(log: ProcessLogger): Stream[String]
Deprecated (renamed). Use lineStream_!(log: ProcessLogger)
instead.
- Annotations
- @ deprecated
- Deprecated
- (Since version 2.11.0) Use stream_! instead.
(defined at scala.sys.process.ProcessBuilder)
Abstract Value Members From scala.sys.process.ProcessBuilder
abstract def #&&(other: ProcessBuilder): ProcessBuilder
Constructs a command that runs this command first and then other
if this
command succeeds.
(defined at scala.sys.process.ProcessBuilder#)
abstract def #|(other: ProcessBuilder): ProcessBuilder
Constructs a command that will run this command and pipes the output to other
.
other
must be a simple command.
(defined at scala.sys.process.ProcessBuilder#)
abstract def #||(other: ProcessBuilder): ProcessBuilder
Constructs a command that runs this command first and then other
if this
command does not succeed.
(defined at scala.sys.process.ProcessBuilder#)
Abstract Value Members From scala.sys.process.ProcessBuilder
abstract def ###(other: ProcessBuilder): ProcessBuilder
Constructs a command that will run this command and then other
. The exit code
will be the exit code of other
.
(defined at scala.sys.process.ProcessBuilder####)
Abstract Value Members From scala.sys.process.ProcessBuilder.Sink
abstract def toSink: ProcessBuilder
- Attributes
- protected
- Definition Classes
- Sink
(defined at scala.sys.process.ProcessBuilder.Sink)
Concrete Value Members From scala.sys.process.ProcessBuilder.Sink
def #<(f: File): ProcessBuilder
Reads the given file into the input stream of this process.
- Definition Classes
- Sink
(defined at scala.sys.process.ProcessBuilder.Sink#)
def #<(b: ProcessBuilder): ProcessBuilder
Reads the output of a scala.sys.process.ProcessBuilder into the input stream of this process.
- Definition Classes
- Sink
(defined at scala.sys.process.ProcessBuilder.Sink#)
def #<(f: URL): ProcessBuilder
Reads the given URL into the input stream of this process.
- Definition Classes
- Sink
(defined at scala.sys.process.ProcessBuilder.Sink#)
def #<(in: ⇒ InputStream): ProcessBuilder
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
(defined at scala.sys.process.ProcessBuilder.Sink#)
Abstract Value Members From scala.sys.process.ProcessBuilder.Source
abstract def toSource: ProcessBuilder
- Attributes
- protected
- Definition Classes
- Source
(defined at scala.sys.process.ProcessBuilder.Source)
Concrete Value Members From scala.sys.process.ProcessBuilder.Source
def cat: ProcessBuilder
Returnes a scala.sys.process.ProcessBuilder representing this Source
.
- Definition Classes
- Source
(defined at scala.sys.process.ProcessBuilder.Source)
Concrete Value Members From scala.sys.process.ProcessBuilder.Source
def #>(f: File): ProcessBuilder
Writes the output stream of this process to the given file.
- Definition Classes
- Source
(defined at scala.sys.process.ProcessBuilder.Source#)
def #>(b: ProcessBuilder): ProcessBuilder
Writes the output stream of this process to a scala.sys.process.ProcessBuilder.
- Definition Classes
- Source
(defined at scala.sys.process.ProcessBuilder.Source#)
def #>(out: ⇒ OutputStream): ProcessBuilder
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
(defined at scala.sys.process.ProcessBuilder.Source#)
def #>>(f: File): ProcessBuilder
Appends the output stream of this process to the given file.
- Definition Classes
- Source (defined at scala.sys.process.ProcessBuilder.Source#)
Full Source:
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