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95 lines
2.2 KiB
Markdown
95 lines
2.2 KiB
Markdown
# Creating a subprocess
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## Concepts
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- Deno is capable of spawning a subprocess via
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[Deno.run](https://doc.deno.land/builtin/stable#Deno.run).
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- `--allow-run` permission is required to spawn a subprocess.
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- Spawned subprocesses do not run in a security sandbox.
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- Communicate with the subprocess via the
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[stdin](https://doc.deno.land/builtin/stable#Deno.stdin),
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[stdout](https://doc.deno.land/builtin/stable#Deno.stdout) and
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[stderr](https://doc.deno.land/builtin/stable#Deno.stderr) streams.
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## Simple example
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This example is the equivalent of running `'echo hello'` from the command line.
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```ts
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/**
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* subprocess_simple.ts
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*/
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// create subprocess
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const p = Deno.run({
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cmd: ["echo", "hello"],
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});
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// await its completion
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await p.status();
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```
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Run it:
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```shell
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$ deno run --allow-run ./subprocess_simple.ts
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hello
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```
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## Security
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The `--allow-run` permission is required for creation of a subprocess. Be aware
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that subprocesses are not run in a Deno sandbox and therefore have the same
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permissions as if you were to run the command from the command line yourself.
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## Communicating with subprocesses
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By default when you use `Deno.run()` the subprocess inherits `stdin`, `stdout`
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and `stderr` of the parent process. If you want to communicate with started
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subprocess you can use `"piped"` option.
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```ts
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/**
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* subprocess.ts
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*/
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const fileNames = Deno.args;
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const p = Deno.run({
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cmd: [
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"deno",
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"run",
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"--allow-read",
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"https://deno.land/std@$STD_VERSION/examples/cat.ts",
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...fileNames,
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],
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stdout: "piped",
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stderr: "piped",
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});
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const { code } = await p.status();
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if (code === 0) {
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const rawOutput = await p.output();
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await Deno.stdout.write(rawOutput);
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} else {
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const rawError = await p.stderrOutput();
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const errorString = new TextDecoder().decode(rawError);
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console.log(errorString);
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}
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Deno.exit(code);
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```
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When you run it:
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```shell
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$ deno run --allow-run ./subprocess.ts <somefile>
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[file content]
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$ deno run --allow-run ./subprocess.ts non_existent_file.md
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Uncaught NotFound: No such file or directory (os error 2)
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at DenoError (deno/js/errors.ts:22:5)
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at maybeError (deno/js/errors.ts:41:12)
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at handleAsyncMsgFromRust (deno/js/dispatch.ts:27:17)
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```
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