When using Bun.spawn(), the stdout of the child process can be consumed as a ReadableStream via proc.stdout.

const proc = Bun.spawn(["echo", "hello"]);

const output = await proc.stdout.text();
output; // => "hello"

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To instead pipe the stdout of the child process to stdout of the parent process, set "inherit".

const proc = Bun.spawn(["echo", "hello"], {
  stdout: "inherit",
});

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See Docs > API > Child processes for complete documentation.