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.

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.

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.

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.

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.

InheritSession makes the new process inherit the terminal session from the parent process. This is the default.

NewSession makes the new process start with a new session without a controlling terminal. On POSIX, setsid is used to create a new process group and session, the pid of the new process is the session id and process group id as well. On Windows DETACHED_PROCESS flag is used to detach the process from inherited console session.

NewConsole creates a new terminal and attaches the process to the new terminal on Windows, using the CREATE_NEW_CONSOLE flag. On POSIX this does nothing.

For Windows see

• https://learn.microsoft.com/en-us/windows/win32/procthread/process-creation-flags
• https://learn.microsoft.com/en-us/windows/console/creation-of-a-console .

For POSIX see, setsid man page.

Define the terminal session behavior for the new process.

Default is InheritSession.

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.

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.

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.

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

Default is True.

An exception that is raised when a process fails.

Since: 0.1.0

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

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

Like toChunks but use the specified configuration to run the process.

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

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

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

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

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

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 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

Like pipeChunks but use the specified configuration to run the process.

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

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

Like toBytesEither 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

Like toChunksEither but use the specified configuration to run the process.

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

Like pipeChunks but also includes stderr as Left stream in the Either output.

Like pipeChunksEither but use the specified configuration to run the process.

Launch a process interfacing with the user. User interrupts are sent to the launched process and ignored by the parent process. The launched process inherits stdin, stdout, and stderr from the parent, so that the user can interact with the process. The parent waits for the child process to exit, an ExitCode is returned when the process finishes.

This is the 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.

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

The ProcessHandle returned can be used to terminate the daemon or send signals to it.

Launch a standalone process i.e. the process does not have a way to attach the IO streams with other processes. The IO streams stdin, stdout, stderr can either be inherited from the parent or closed.

This API is more powerful than interactive and daemon and can be used to implement both of these. However, it should be used carefully e.g. if you inherit the IO streams and parent is not waiting for the child process to finish then both parent and child may use the IO streams resulting in garbled IO if both are reading/writing simultaneously.

If the parent chooses to wait for the process an ExitCode is returned otherwise a ProcessHandle is returned which can be used to terminate the process, send signals to it or wait for it to finish.