BaseOptions.onExit method | Bun module | Bun

Callback that runs when the Subprocess exits

This is called even if the process exits with a non-zero exit code.

Warning: this may run before the Bun.spawn function returns.

A simple alternative is await subprocess.exited.

If an error occurred in the call to waitpid2, this will be the error.

const subprocess = spawn({
cmd: ["echo", "hello"],
onExit: (subprocess, code) => {
console.log(`Process exited with code ${code}`);
},
});

A process created by Bun.spawn.

This type accepts 3 optional type parameters which correspond to the stdio array from the options object. Instead of specifying these, you should use one of the following utility types instead:

Synchronously get the exit code of the process

If the process hasn't exited yet, this will return null

The exit code of the process

The promise will resolve when the process exits

Has the process exited?

The process ID of the child process

const { pid } = Bun.spawn({ cmd: ["echo", "hello"] });
console.log(pid); // 1234

This returns the same value as Subprocess.stdout

It exists for compatibility with ReadableStream.pipeThrough

Synchronously get the signal code of the process

If the process never sent a signal code, this will return null

To receive signal code changes, use the onExit callback.

If the signal code is unknown, it will return the original signal code number, but that case should essentially never happen.

Access extra file descriptors passed to the stdio option in the options object.

Entries beyond index 2 are number for "pipe" slots and, on POSIX, for slots where a raw file descriptor was supplied (the same fd is returned; it remains owned by the caller and is never closed by the subprocess). Other slots — including raw fds on Windows — are null.

The terminal attached to this subprocess, if spawned with the terminal option. Returns undefined if no terminal was attached.

When a terminal is attached, stdin, stdout, and stderr return null. Use terminal.write() and the data callback instead.

const proc = Bun.spawn(["bash"], {
terminal: { data: (term, data) => console.log(data.toString()) },
});

proc.terminal?.write("echo hello\n");

Disconnect the IPC channel to the subprocess. This is only supported if the subprocess was created with the ipc option.

Kill the process

The exitCode to send to the process

This method will tell Bun to wait for this process to exit after you already called unref().

Before shutting down, Bun will wait for all subprocesses to exit by default

Get the resource usage information of the process (max RSS, CPU time, etc)

Only available after the process has exited

If the process hasn't exited yet, this will return undefined

Send a message to the subprocess. This is only supported if the subprocess was created with the ipc option, and is another instance of bun.

Messages are serialized using the JSC serialize API, which allows for the same types that postMessage/structuredClone supports.

Before shutting down, Bun will wait for all subprocesses to exit by default

This method will tell Bun to not wait for this process to exit before shutting down.

The cause of the error.