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deno-proc

Running child processes should not be difficult. proc attempts to bring the ease of bash scripting to Deno.

documentation

deno doc -q https://deno.land/x/proc/mod.ts

Key Concepts

Leaking Resources

One of the challenges of working with processes in Deno is that you must manually close every process resource - readers, writers, and the process itself. Additionally, it is an error (with real consequences) to attempt to try to close an already closed resource again. This can make working with even one process somewhat awkward and tricky. With more than one process, it is confusing and maybe a bit dangerous.

To help with this problem, proc introduces ProcGroup. A ProcGroup is a Deno.Closer, and when you close it, you also close all resources associated with the group.

proc requires that all processes it manages are associated with a ProcGroup.

const pg = procgroup();
try {
  console.log(
    await proc(EmptyInput(), StringOutput()).run(pg, {
      cmd: ["ls", "-la"],
    }),
  );
} finally {
  pg.close();
}

Input and Output Types

Raw stdin, stdout, and stderr from a process are streamed byte data. This is a simple definition, but it is not very useful. We need to be able to interpret data differently in different circumstances.

Streamed byte data is the fastest, so if we are just piping bytes from one process to another, we would use BytesIterableOutput() for stdout of process #1 and BytesIterableInput() for stdin of process #2.

If you have a small amount of data (it can be kept in memory), StringInput() and StringOutput() let you work with string data. For text data that is too big to fit in memory, or if you just want to work with real-time streamed text data, use StringIterableInput() and StringIterableOutput(). There is some overhead associated with processing streamed bytes into text lines, but this is how you will interact with process input and output much of the time.

An Example

This example shows how proc(...) is used to generate a process definition. In this case, I am going to pass in a string and get back a Uint8Array. gzip is just getting a stream of bytes in both cases of course. Our definition is translating for us.

/**
 * Use `gzip` to compress some text.
 * @param text The text to compress.
 * @return The text compressed into bytes.
 */
async function gzip(text: string): Promise<Uint8Array> {
  const pg = procgroup();
  try {
    /* I am using a string for input and a Uint8Array (bytes) for output. */
    const processDef: Proc<string, Uint8Array> = proc(
      StringInput(),
      BytesOutput(),
    );

    return await processDef.run(pg, {
      cmd: ["gzip", "-c"],
    }, text);
  } finally {
    pg.close();
  }
}

const pg = procgroup();
try {
  console.dir(await gzip("Hello, world."));
} finally {
  pg.close();
}

Input Types

^* - ReaderInput is a special input type that does not have a corresponding output type. It is not useful for piping data from process to process.

Output Types

^* - Special output type that mixes stdout and stderr together. stdout must be text data.

Examples

Run an Inline Bash Script

Starting with something simple yet useful, this is an example of running a bash script using proc.

const pg = procgroup();
try {
  console.log(
    await proc(EmptyInput(), StringOutput()).run(pg, {
      cmd: [
        "/bin/bash",
        "--login",
        "-c",
        "echo 'Hello, Deno.'",
      ],
    }),
  );
} finally {
  pg.close();
}