ChildProcess unstable

Describes child processes before they are started.

A Command stores the executable, arguments, environment, standard streams, working directory, and other process options. Commands can also be piped together. A command is an Effect; running it asks the ChildProcessSpawner service to start the process and returns a ChildProcessHandle.

28 exports Since v4.0.0 Source

Combinators

pipeTo

unstable

Since v4.0.0

Pipes the output of one command to the input of another.

Details

By default, pipes stdout from the source to stdin of the destination. Use the options parameter to customize which streams are connected.

Signature

declare const pipeTo: {
  (that: Command, options?: PipeOptions): (self: Command) => PipedCommand;
  (self: Command, that: Command, options?: PipeOptions): PipedCommand;
}

Example Piping command output

import { ChildProcess } from "effect/process"

// Pipe stdout (default)
const pipeline1 = ChildProcess.make`cat file.txt`.pipe(
  ChildProcess.pipeTo(ChildProcess.make`grep pattern`)
)

// Pipe stderr instead of stdout
const pipeline2 = ChildProcess.make`my-program`.pipe(
  ChildProcess.pipeTo(ChildProcess.make`grep error`, { from: "stderr" })
)

// Pipe combined stdout and stderr
const pipeline3 = ChildProcess.make`my-program`.pipe(
  ChildProcess.pipeTo(ChildProcess.make`tee output.log`, { from: "all" })
)

const result = [pipeline1._tag, pipeline2.options.from, pipeline3.options.from]
result // => ["PipedCommand", "stderr", "all"]

prefix

unstable

Since v4.0.0

Prepends another command to a command.

Details

For pipelines, only the leftmost command is prefixed.

Signature

declare const prefix: {
  (command: string, args?: readonly Array<string>): (self: Command) => Command;
  (templates: TemplateStringsArray, ...expressions: readonly Array<TemplateExpression>): (self: Command) => Command;
  (self: Command, command: string, args?: readonly Array<string>): Command;
}

Example Prefixing commands

import { ChildProcess } from "effect/process"

const command = ChildProcess.make`echo "foo"`

const prefixed = command.pipe(
  ChildProcess.prefix`time`
)

// now prefixed will execute `time echo "foo"`
const result = prefixed._tag === "StandardCommand" ? `${prefixed.command} ${prefixed.args[0]}` : prefixed._tag
result // => "time echo"

setCwd

unstable

Since v4.0.0

Sets the current working directory for a command.

Details

For pipelines, applies to each command in the pipeline.

Signature

declare const setCwd: {
  (cwd: string): (self: Command) => Command;
  (self: Command, cwd: string): Command;
}

Example Setting command working directories

import { ChildProcess } from "effect/process"

const cmd = ChildProcess.make`ls -la`.pipe(
  ChildProcess.setCwd("/tmp")
)
const result = cmd._tag === "StandardCommand" && cmd.options.cwd // => "/tmp"

setEnv

unstable

Since v4.0.0

Adds environment variables to a command, merging them with any existing command environment and overriding duplicate keys.

Details

For pipelines, applies to each command in the pipeline.

Signature

declare const setEnv: {
  (env: Record<string, string>): (self: Command) => Command;
  (self: Command, env: Record<string, string>): Command;
}

Example Setting command environment variables

import { ChildProcess } from "effect/process"

const cmd = ChildProcess.make`node script.js`.pipe(
  ChildProcess.setEnv({ NODE_ENV: "test" })
)
const result = cmd._tag === "StandardCommand" && cmd.options.env?.NODE_ENV // => "test"

Constructors

make

unstable

Since v4.0.0

Create a command from a template literal, options + template, or array form.

Details

This function supports three calling conventions:

Template literal: make\npm run build``
Options + template literal: make({ cwd: "/app" })\npm run build``
Array form: make("npm", ["run", "build"], options?)

Template literals are not parsed until execution time, allowing parsing errors to flow through Effect's error channel.

Signature

declare const make: {
  (command: string, options?: CommandOptions): StandardCommand;
  (command: string, args: readonly Array<string>, options?: CommandOptions): StandardCommand;
  (options: CommandOptions): (templates: TemplateStringsArray, ...expressions: readonly Array<TemplateExpression>) => StandardCommand;
  (templates: TemplateStringsArray, ...expressions: readonly Array<TemplateExpression>): StandardCommand;
}

Example Creating commands

import { ChildProcess } from "effect/process"

// Template literal form
const cmd1 = ChildProcess.make`echo "hello"`

// With options
const cmd2 = ChildProcess.make({ cwd: "/tmp" })`ls -la`

// Array form
const cmd3 = ChildProcess.make("git", ["status"])

const result = [cmd1.command, cmd2.options.cwd, cmd3.args[0]] // => ["echo", "/tmp", "status"]

Converting

fdName

unstable

Since v4.0.0

Create an fd name from its numeric index.

Signature

declare function fdName(fd: number): string

parseFdName

unstable

Since v4.0.0

Parses an fd name like "fd3" to its numeric index. Returns undefined if the name is invalid.

Signature

declare function parseFdName(name: string): number | undefined

Guards

isCommand

unstable

Since v4.0.0

Checks whether a value is a Command.

Signature

declare function isCommand(u: unknown): u is Command

isPipedCommand

unstable

Since v4.0.0

Checks whether a command is a PipedCommand.

Signature

declare function isPipedCommand(command: Command): command is PipedCommand

isStandardCommand

unstable

Since v4.0.0

Checks whether a command is a StandardCommand.

Signature

declare function isStandardCommand(command: Command): command is StandardCommand

Models

AdditionalFdConfig

type unstable

Since v4.0.0

Configuration for additional file descriptors to expose to the child process.

Signature

type AdditionalFdConfig = {
  readonly stream?: Stream.Stream<Uint8Array, PlatformError.PlatformError>;
  readonly type: "input";
} | {
  readonly sink?: Sink.Sink<Uint8Array, Uint8Array, never, PlatformError.PlatformError>;
  readonly type: "output";
}

Command

type unstable

Since v4.0.0

A command that can be built using make, combined using pipeTo, and executed using exec or spawn.

Signature

type Command = StandardCommand | PipedCommand

CommandInput

type unstable

Since v4.0.0

Input type for child process stdin.

Signature

type CommandInput = "pipe" | "inherit" | "ignore" | "overlapped" | Stream.Stream<Uint8Array, PlatformError.PlatformError>

CommandOutput

type unstable

Since v4.0.0

Output type for child process stdout/stderr.

Signature

type CommandOutput = "pipe" | "inherit" | "ignore" | "overlapped" | Sink.Sink<Uint8Array, Uint8Array, never, PlatformError.PlatformError>

Encoding

type unstable

Since v4.0.0

The encoding format to use for binary data.

Signature

type Encoding = "ascii" | "utf8" | "utf-8" | "utf16le" | "utf-16le" | "ucs2" | "ucs-2" | "base64" | "base64url" | "latin1" | "binary" | "hex"

PipedCommand

interface unstable

Since v4.0.0

A pipeline of commands where the output of one is piped to the input of the next.

Signature

interface PipedCommand extends Effect<ChildProcessHandle, PlatformError.PlatformError, ChildProcessSpawner | Scope.Scope> {
  readonly _tag: "PipedCommand";
  readonly left: Command;
  readonly options: PipeOptions;
  readonly right: Command;
}

PipeFromOption

type unstable

Since v4.0.0

Specifies which stream to pipe from the source subprocess.

Details

"stdout": Pipe stdout from the source (default)
"stderr": Pipe stderr from the source
"all": Pipe both stdout and stderr interleaved
`fd${number}`: Pipe from a custom file descriptor (e.g., "fd3")

Signature

type PipeFromOption = "stdout" | "stderr" | "all" | `fd${number}`

PipeToOption

type unstable

Since v4.0.0

Specifies which input to pipe to on the destination subprocess.

Details

"stdin": Pipe to stdin of the destination (default)
`fd${number}`: Pipe to a custom file descriptor (e.g., "fd3")

Signature

type PipeToOption = "stdin" | `fd${number}`

Signal

type unstable

Since v4.0.0

A signal that can be sent to a child process.

Signature

type Signal = "SIGABRT" | "SIGALRM" | "SIGBUS" | "SIGCHLD" | "SIGCONT" | "SIGFPE" | "SIGHUP" | "SIGILL" | "SIGINT" | "SIGIO" | "SIGIOT" | "SIGKILL" | "SIGPIPE" | "SIGPOLL" | "SIGPROF" | "SIGPWR" | "SIGQUIT" | "SIGSEGV" | "SIGSTKFLT" | "SIGSTOP" | "SIGSYS" | "SIGTERM" | "SIGTRAP" | "SIGTSTP" | "SIGTTIN" | "SIGTTOU" | "SIGUNUSED" | "SIGURG" | "SIGUSR1" | "SIGUSR2" | "SIGVTALRM" | "SIGWINCH" | "SIGXCPU" | "SIGXFSZ" | "SIGBREAK" | "SIGLOST" | "SIGINFO"

StandardCommand

interface unstable

Since v4.0.0

A standard command with pre-parsed command and arguments.

Signature

interface StandardCommand extends Effect<ChildProcessHandle, PlatformError.PlatformError, ChildProcessSpawner | Scope.Scope> {
  readonly _tag: "StandardCommand";
  readonly args: readonly Array<string>;
  readonly command: string;
  readonly options: CommandOptions;
}

StderrConfig

interface unstable

Since v4.0.0

Configuration for the child process standard error stream.

Signature

interface StderrConfig {
  readonly stream?: CommandOutput;
}

StdinConfig

interface unstable

Since v4.0.0

Configuration for the child process standard input stream.

Signature

interface StdinConfig {
  readonly encoding?: Encoding;
  readonly endOnDone?: boolean;
  readonly stream: CommandInput;
}

StdoutConfig

interface unstable

Since v4.0.0

Configuration for the child process standard output stream.

Signature

interface StdoutConfig {
  readonly stream?: CommandOutput;
}

TemplateExpression

type unstable

Since v4.0.0

Template expression type for interpolated values.

Signature

type TemplateExpression = TemplateExpressionItem | ReadonlyArray<TemplateExpressionItem>

TemplateExpressionItem

type unstable

Since v4.0.0

Valid template expression item types.

Signature

type TemplateExpressionItem = string | number | boolean

Options

CommandOptions

interface unstable

Since v4.0.0

Options for command execution.

Signature

interface CommandOptions extends KillOptions {
  readonly additionalFds?: Record<`fd${number}`, AdditionalFdConfig>;
  readonly cwd?: string;
  readonly detached?: boolean;
  readonly env?: Record<string, string | undefined>;
  readonly extendEnv?: boolean;
  readonly shell?: string | boolean;
  readonly stderr?: CommandOutput | StderrConfig;
  readonly stdin?: StdinConfig | CommandInput;
  readonly stdout?: StdoutConfig | CommandOutput;
  readonly windowsHide?: boolean;
}

KillOptions

interface unstable

Since v4.0.0

Options that can be used to control how a child process is terminated.

Signature

interface KillOptions {
  readonly forceKillAfter?: Input;
  readonly killSignal?: Signal;
}

PipeOptions

interface unstable

Since v4.0.0

Options for controlling how commands are piped together.

Signature

interface PipeOptions {
  readonly from?: PipeFromOption;
  readonly to?: PipeToOption;
}

Example Piping stderr between commands

import { ChildProcess } from "effect/process"

// Pipe stderr instead of stdout
const pipeline = ChildProcess.make`my-program`.pipe(
  ChildProcess.pipeTo(ChildProcess.make`grep error`, { from: "stderr" })
)
const result = [pipeline._tag, pipeline.options.from] // => ["PipedCommand", "stderr"]