Streamly.Internal.System.Process

Process Configuration

data Config

Process configuration used for creating a new process.

By default the process config is setup to inherit the following attributes from the parent process:

• Current working directory
• Environment variables
• Open file descriptors
• Process group
• Terminal session

On POSIX:

• Process uid and gid
• Signal handlers

On Windows by default the parent process waits for the entire child process tree to finish.

Common Config Options

These options apply to both POSIX and Windows.

setCwd :: Maybe FilePath -> Config -> Config

Set the current working directory of the new process. When Nothing, the working directory is inherited from the parent process.

Default is Nothing - inherited from the parent process.

setEnv :: Maybe [(String, String)] -> Config -> Config

Set the environment variables for the new process. When Nothing, the environment is inherited from the parent process.

Default is Nothing - inherited from the parent process.

closeFiles :: Bool -> Config -> Config

Close all open file descriptors inherited from the parent process. Note, this does not apply to stdio descriptors - the behavior of those is determined by other configuration settings.

Default is False.

Note: if the number of open descriptors is large, it may take a while closing them.

newProcessGroup :: Bool -> Config -> Config

If True the new process starts a new process group, becomes a process group leader, its pid becoming the process group id.

See the POSIX setpgid man page.

Default is False, the new process belongs to the parent's process group.

setSession :: Session -> Config -> Config

Define the terminal session behavior for the new process.

Default is InheritSession.

Posix Only Options

These options have no effect on Windows.

parentIgnoresInterrupt :: Bool -> Config -> Config

When this is True, the parent process ignores user interrupt signals SIGINT and SIGQUIT delivered to it until the child process exits. If multiple child processes are started then the default handling in the parent is restored only after the last one exits.

When a user presses CTRL-C or CTRL- on the terminal, a SIGINT or SIGQUIT is sent to all the foreground processes in the terminal session, this includes both the child and the parent. By default, on receiving these signals, the parent process would cleanup and exit, to avoid that and let the child handle these signals we can choose to ignore these signals in the parent until the child exits.

POSIX only. Default is False.

setUserId :: Maybe Word32 -> Config -> Config

Use the POSIX setuid call to set the user id of the new process before executing the command. The parent process must have sufficient privileges to set the user id.

POSIX only. See the POSIX setuid man page.

Default is Nothing - inherit from the parent.

setGroupId :: Maybe Word32 -> Config -> Config

Use the POSIX setgid call to set the group id of the new process before executing the command. The parent process must have sufficient privileges to set the group id.

POSIX only. See the POSIX setgid man page.

Default is Nothing - inherit from the parent.

Windows Only Options

These options have no effect on Posix.

waitForChildTree :: Bool -> Config -> Config

On Windows, the parent waits for the entire tree of process i.e. including processes that are spawned by the child process.

Default is True.

Internal

inheritStdin :: Config -> Config

inheritStdout :: Config -> Config

pipeStdErr :: Config -> Config

Exceptions

newtype ProcessFailure

An exception that is raised when a process fails.

Since: 0.1.0

Constructors

ProcessFailure Int

The exit code of the process.

Instances

Exception ProcessFailure

Defined in Streamly.Internal.System.Process

Methods

toException :: ProcessFailure -> SomeException

fromException :: SomeException -> Maybe ProcessFailure

displayException :: ProcessFailure -> String

Show ProcessFailure

Defined in Streamly.Internal.System.Process

Methods

showsPrec :: Int -> ProcessFailure -> ShowS

show :: ProcessFailure -> String

showList :: [ProcessFailure] -> ShowS

Generation

stdout of the process is redirected to output stream.

toBytes

Arguments

:: (MonadAsync m, MonadCatch m)

=> FilePath

Executable name or path

-> [String]

Arguments

-> Stream m Word8

Output Stream

The following code is equivalent to the shell command echo "hello world":

>>> :{
   Process.toBytes "echo" ["hello world"]
 & Stream.fold Stdio.write
 :}
hello world

Since: 0.1.0

toChunks

Arguments

:: (MonadAsync m, MonadCatch m)

=> FilePath

Executable name or path

-> [String]

Arguments

-> Stream m (Array Word8)

Output Stream

The following code is equivalent to the shell command echo "hello world":

>>> :{
   Process.toChunks "echo" ["hello world"]
 & Stream.fold Stdio.writeChunks
 :}
hello world

>>> toChunks = toChunksWith id

Since: 0.1.0

toChunksWith

Arguments

:: (MonadCatch m, MonadAsync m)

=> (Config -> Config)

Config modifier

-> FilePath

Executable name or path

-> [String]

Arguments

-> Stream m (Array Word8)

Output stream

toChars

Arguments

:: (MonadAsync m, MonadCatch m)

=> FilePath

Executable name or path

-> [String]

Arguments

-> Stream m Char

Output Stream

>>> toChars path args = toBytes path args & Unicode.decodeUtf8

toLines

Arguments

:: (MonadAsync m, MonadCatch m)

=> Fold m Char a

-> FilePath

Executable name or path

-> [String]

Arguments

-> Stream m a

Output Stream

>>> toLines path args f = toChars path args & Unicode.lines f

toString

Arguments

:: (MonadAsync m, MonadCatch m)

=> FilePath

Executable name or path

-> [String]

Arguments

-> m String

>>> toString path args = toChars path args & Stream.fold Fold.toList

toStdout

Arguments

:: (MonadAsync m, MonadCatch m)

=> FilePath

Executable name or path

-> [String]

Arguments

-> m ()

>>> toStdout path args = toChunks path args & Stdio.putChunks

toNull

Arguments

:: (MonadAsync m, MonadCatch m)

=> FilePath

Executable name or path

-> [String]

Arguments

-> m ()

>>> toNull path args = toChunks path args & Stream.fold Fold.drain

Transformation

The input stream is redirected to the stdin of the process, stdout of the process is redirected to the output stream.

pipeBytes

Arguments

:: (MonadCatch m, MonadAsync m)

=> FilePath

Executable name or path

-> [String]

Arguments

-> Stream m Word8

Input Stream

-> Stream m Word8

Output Stream

Like pipeChunks except that it works on a stream of bytes instead of a stream of chunks.

We can write the example in pipeChunks as follows.

>>> :{
   Process.toBytes "echo" ["hello world"]
 & Process.pipeBytes "tr" ["[a-z]", "[A-Z]"]
 & Stream.fold Stdio.write
 :}
HELLO WORLD

pre-release

pipeChunks

Arguments

:: (MonadCatch m, MonadAsync m)

=> FilePath

Executable name or path

-> [String]

Arguments

-> Stream m (Array Word8)

Input stream

-> Stream m (Array Word8)

Output stream

pipeChunks file args input runs the executable file specified by its name or path using args as arguments and input stream as its standard input. Returns the standard output of the executable as a stream.

If only the name of an executable file is specified instead of its path then the file name is searched in the directories specified by the PATH environment variable.

If the input stream throws an exception or if the output stream is garbage collected before it could finish then the process is terminated with SIGTERM.

If the process terminates with a non-zero exit code then a ProcessFailure exception is raised.

The following code is equivalent to the shell command echo "hello world" | tr [a-z] [A-Z]:

>>> :{
   Process.toChunks "echo" ["hello world"]
 & Process.pipeChunks "tr" ["[a-z]", "[A-Z]"]
 & Stream.fold Stdio.writeChunks
 :}
HELLO WORLD

pre-release

pipeChunksWith

Arguments

:: (MonadCatch m, MonadAsync m)

=> (Config -> Config)

Config modifier

-> FilePath

Executable name or path

-> [String]

Arguments

-> Stream m (Array Word8)

Input stream

-> Stream m (Array Word8)

Output stream

pipeChars

Arguments

:: (MonadCatch m, MonadAsync m)

=> FilePath

Executable name or path

-> [String]

Arguments

-> Stream m Char

Input Stream

-> Stream m Char

Output Stream

Like pipeChunks except that it works on a stream of chars instead of a stream of chunks.

>>> :{
   Process.toChars "echo" ["hello world"]
 & Process.pipeChars "tr" ["[a-z]", "[A-Z]"]
 & Stdio.putChars
 :}
HELLO WORLD

We can seamlessly replace the tr process with the Haskell toUpper function:

>>> :{
   Process.toChars "echo" ["hello world"]
 & fmap toUpper
 & Stdio.putChars
 :}
HELLO WORLD

pre-release

Stderr

Like other Generation routines but along with stdout, stderr is also included in the output stream. stdout is converted to Right values in the output stream and stderr is converted to Left values.

toBytesEither

Arguments

:: (MonadAsync m, MonadCatch m)

=> FilePath

Executable name or path

-> [String]

Arguments

-> Stream m (Either Word8 Word8)

Output Stream

toBytesEither path args runs the executable at path using args as arguments and returns a stream of Either bytes. The Left values are from stderr and the Right values are from stdout of the executable.

Raises ProcessFailure exception in case of failure.

The following example uses echo to write hello to stdout and world to stderr, then uses folds from Streamly.Console.Stdio to write them back to stdout and stderr respectively:

>>> :{
  Process.toBytesEither "/bin/bash" ["-c", "echo 'hello'; echo 'world' 1>&2"]
& Stream.fold (Fold.partition Stdio.writeErr Stdio.write)
:}
world
hello
((),())

Since: 0.1.0

toChunksEither

Arguments

:: (MonadAsync m, MonadCatch m)

=> FilePath

Executable name or path

-> [String]

Arguments

-> Stream m (Either (Array Word8) (Array Word8))

Output Stream

Like toBytes but generates a stream of Array Word8 instead of a stream of Word8.

>>> :{
  toChunksEither "bash" ["-c", "echo 'hello'; echo 'world' 1>&2"]
& Stream.fold (Fold.partition Stdio.writeErrChunks Stdio.writeChunks)
:}
world
hello
((),())

>>> toChunksEither = toChunksEitherWith id

Prefer 'toChunksEither over 'toBytesEither when performance matters.

Pre-release

toChunksEitherWith

Arguments

:: (MonadCatch m, MonadAsync m)

=> (Config -> Config)

Config modifier

-> FilePath

Executable name or path

-> [String]

Arguments

-> Stream m (Either (Array Word8) (Array Word8))

Output stream

pipeBytesEither

Arguments

:: (MonadCatch m, MonadAsync m)

=> FilePath

Executable name or path

-> [String]

Arguments

-> Stream m Word8

Input Stream

-> Stream m (Either Word8 Word8)

Output Stream

pipeBytesEither path args input runs the executable at path using args as arguments and input stream as its standard input. The error stream of the executable is presented as Left values in the resulting stream and output stream as Right values.

Raises ProcessFailure exception in case of failure.

For example, the following is equivalent to the shell command echo "hello world" | tr [:lower:] [:upper:]:

>>> :{
   pipeBytesEither "echo" ["hello world"] Stream.nil
 & Stream.catRights
 & pipeBytesEither "tr" ["[:lower:]", "[:upper:]"]
 & Stream.catRights
 & Stream.fold Stdio.write
 :}
HELLO WORLD

Since: 0.1.0

pipeChunksEither

Arguments

:: (MonadCatch m, MonadAsync m)

=> FilePath

Executable name or path

-> [String]

Arguments

-> Stream m (Array Word8)

Input stream

-> Stream m (Either (Array Word8) (Array Word8))

Output stream

pipeChunksEitherWith

Arguments

:: (MonadCatch m, MonadAsync m)

=> (Config -> Config)

Config modifier

-> FilePath

Executable name or path

-> [String]

Arguments

-> Stream m (Array Word8)

Input stream

-> Stream m (Either (Array Word8) (Array Word8))

Output stream

Standalone Processes

standalone

Arguments

:: Bool

Wait for process to finish?

-> (Bool, Bool, Bool)

close (stdin, stdout, stderr)

-> (Config -> Config)

-> FilePath

Executable name or path

-> [String]

Arguments

-> IO (Either ExitCode ProcessHandle)

interactive

Arguments

:: (Config -> Config)

-> FilePath

Executable name or path

-> [String]

Arguments

-> IO ExitCode

Inherits stdin, stdout, and stderr from the parent, so that the user can interact with the process, user interrupts are handled by the child process, the parent waits for the child process to exit.

This is same as the common system function found in other libraries used to execute commands.

On Windows you can pass setSession NewConsole to create a new console.

daemon

Arguments

:: (Config -> Config)

-> FilePath

Executable name or path

-> [String]

Arguments

-> IO ProcessHandle

Closes stdin, stdout and stderr, creates a new session, detached from the terminal, the parent does not wait for the process to finish.

Deprecated

processBytes

Arguments

:: (MonadCatch m, MonadAsync m)

=> FilePath

Executable name or path

-> [String]

Arguments

-> Stream m Word8

Input Stream

-> Stream m Word8

Output Stream

Deprecated: Please use pipeBytes instead.

processChunks

Arguments

:: (MonadCatch m, MonadAsync m)

=> FilePath

Executable name or path

-> [String]

Arguments

-> Stream m (Array Word8)

Input stream

-> Stream m (Array Word8)

Output stream

Deprecated: Please use pipeChunks instead.