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For CLI tools, it’s often useful to read from stdin. In Bun, the console object is an AsyncIterable that yields lines from stdin.

index.ts

const prompt = "Type something: ";
process.stdout.write(prompt);
for await (const line of console) {
  console.log(`You typed: ${line}`);
  process.stdout.write(prompt);
}

Running this file results in a never-ending interactive prompt that echoes whatever the user types.

terminal

bun run index.ts

Type something: hello
You typed: hello
Type something: hello again
You typed: hello again

Bun also exposes stdin as a BunFile via Bun.stdin. This is useful for incrementally reading large inputs that are piped into the bun process. There is no guarantee that the chunks will be split line-by-line.

stdin.ts

for await (const chunk of Bun.stdin.stream()) {
  // chunk is Uint8Array
  // this converts it to text (assumes ASCII encoding)
  const chunkText = Buffer.from(chunk).toString();
  console.log(`Chunk: ${chunkText}`);
}

This will print the input that is piped into the bun process.

terminal

echo "hello" | bun run stdin.ts

Chunk: hello

See Docs > API > Utils for more useful utilities.

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Spawn a child process and communicate using IPC

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