Google zx

#!/usr/bin/env zx
await $`cat package.json | grep name`;
let branch = await $`git branch --show-current`;
await $`dep deploy --branch=${branch}`;
await Promise.all([$`sleep 1; echo 1`, $`sleep 2; echo 2`, $`sleep 3; echo 3`]);
let name = "foo bar";
await $`mkdir /tmp/${name}`;

Bash is great, but when it comes to writing scripts, people usually choose a more convenient programming language. JavaScript is a perfect choice, but standard Node.js library requires additional hassle before using. The zx package provides useful wrappers around child_process, escapes arguments and gives sensible defaults.

Install

npm i -g zx

Requirement

Node.js >= 14.8.0

Documentation

Write your scripts in a file with .mjs extension in order to be able to use await on top level. If you prefer the .js extension, wrap your scripts in something like void async function () {...}(). Add the following shebang to the beginning of your zx scripts:

#!/usr/bin/env zx

Now you will be able to run your script like so:

chmod +x ./script.mjs
./script.mjs

Or via the zx executable:

zx ./script.mjs

All functions ($, cd, fetch, etc) are available straight away without any imports.

$`command`

Executes a given string using the spawn function from the child_process package and returns ProcessPromise<ProcessOutput>. Everything passed through ${...} will be automatically escaped and quoted.

let name = "foo & bar";
await $`mkdir ${name}`;

There is no need to add extra quotes. Read more about it in quotes. You can pass an array of arguments if needed:

let flags = ["--oneline", "--decorate", "--color"];
await $`git log ${flags}`;

If the executed program returns a non-zero exit code, ProcessOutput will be thrown.

try {
await $`exit 1`;
} catch (p) {
console.log(`Exit code: ${p.exitCode}`);
console.log(`Error: ${p.stderr}`);
}

`ProcessPromise`

class ProcessPromise<T> extends Promise<T> {
readonly stdin: Writable;
readonly stdout: Readable;
readonly stderr: Readable;
readonly exitCode: Promise<number>;
pipe(dest): ProcessPromise<T>;
kill(signal = "SIGTERM"): Promise<void>;
}

The pipe() method can be used to redirect stdout:

await $`cat file.txt`.pipe(process.stdout);

`ProcessOutput`

class ProcessOutput {
readonly stdout: string;
readonly stderr: string;
readonly exitCode: number;
toString(): string;
}

Functions

`cd()`

Changes the current working directory.

cd("/tmp");
await $`pwd`; // outputs /tmp

`fetch()`

A wrapper around the node-fetch package.

let resp = await fetch("http://wttr.in");
if (resp.ok) {
console.log(await resp.text());
}

`question()`

A wrapper around the readline package. Usage:

let bear = await question("What kind of bear is best? ");
let token = await question("Choose env variable: ", {
choices: Object.keys(process.env),
});

In second argument, array of choices for Tab autocompletion can be specified.

function question(query?: string, options?: QuestionOptions): Promise<string>;
type QuestionOptions = { choices: string[] };

`sleep()`

A wrapper around the setTimeout function.

await sleep(1000);

`nothrow()`

Changes behavior of $ to not throw an exception on non-zero exit codes.

function nothrow<P>(p: P): P;

Usage:

await nothrow($`grep something from-file`);
// Inside a pipe():
await $`find ./examples -type f -print0`
.pipe(nothrow($`xargs -0 grep something`))
.pipe($`wc -l`);

If only the exitCode is needed, you can use the next code instead:

if (await $`[[ -d path ]]`.exitCode == 0) {
...
}
// Equivalent of:
if ((await nothrow($`[[ -d path ]]`)).exitCode == 0) {
...
}

Packages

Next packages is available without importing inside scripts.

`chalk` package

The chalk package.

console.log(chalk.blue("Hello world!"));

`fs` package

The fs-extra package.

let content = await fs.readFile("./package.json");

`globby` package

The globby package.

let packages = await globby(["package.json", "packages/*/package.json"]);
let pictures = globby.globbySync("content/*.(jpg|png)");

Also, globby available via the glob shortcut:

await $`svgo ${await glob("*.svg")}`;

`os` package

The os package.

await $`cd ${os.homedir()} && mkdir example`;

`path` package

The path package.

await $`mkdir ${path.join(basedir, "output")}`;

`minimist` package

The minimist package. Available as global const argv.

Configuration

`$.shell`

Specifies what shell is used. Default is which bash.

$.shell = "/usr/bin/bash";

Or use a CLI argument: --shell=/bin/bash

`$.prefix`

Specifies the command that will be prefixed to all commands run. Default is set -euo pipefail;. Or use a CLI argument: --prefix='set -e;'

`$.quote`

Specifies a function for escaping special characters during command substitution.

`$.verbose`

Specifies verbosity. Default is true. In verbose mode, the zx prints all executed commands alongside with their outputs. Or use a CLI argument --quiet to set $.verbose = false.

Polyfills

`filename` & `dirname`

In ESM modules, Node.js does not provide __filename and __dirname globals. As such globals are really handy in scripts, zx provides these for use in .mjs files (when using the zx executable).

`require()`

In ESM modules, the require() function is not defined. The zx provides require() function, so it can be used with imports in .mjs files (when using zx executable).

let { version } = require("./package.json");

FAQ

Passing env variables

process.env.FOO = "bar";
await $`echo $FOO`;

Passing array of values

If array of values passed as argument to $, items of the array will be escaped individually and concatenated via space. Example:

let files = [...]
await $`tar cz ${files}`

Importing from other scripts

It is possible to make use of $ and other functions via explicit imports:

#!/usr/bin/env node
import { $ } from "zx";
await $`date`;

Scripts without extensions

If script does not have a file extension (like .git/hooks/pre-commit), zx assumes that it is an ESM module.

Markdown scripts

The zx can execute scripts written in markdown (docs/markdown.md):

zx docs/markdown.md

TypeScript scripts

The zx can compile .ts scripts to .mjs and execute them.

zx script.ts

Example:

import { $ } from "zx";
void (async function () {
await $`ls -la`;
})();

Executing remote scripts

If the argument to the zx executable starts with https://, the file will be downloaded and executed.

zx https://medv.io/example-script.mjs

zx https://medv.io/game-of-life.mjs

Executing scripts from stdin

The zx supports executing scripts from stdin.

zx << "EOF";
await $`pwd`;
EOF;

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