#!/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 more complex scripts, many people prefer a more convenient programming language. JavaScript is a perfect choice, but the Node.js standard library requires additional hassle before using. The zx package provides useful wrappers around child_process, escapes arguments and gives sensible defaults.

npm i -g zx

Requirement: Node version >= 16.0.0

$ · cd() · fetch() · question() · sleep() · echo() · stdin() · within() · retry() · spinner() · chalk · fs · os · path · glob · yaml · minimist · which · __filename · __dirname · require()

For running commands on remote hosts, see webpod.

Write your scripts in a file with an .mjs extension in order to use await at the 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.

Or import globals explicitly (for better autocomplete in VS Code).

import 'zx/globals'

Executes a given command using the spawn func and returns ProcessPromise.

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}`)
}

class ProcessPromise extends Promise<ProcessOutput> {
  stdin: Writable
  stdout: Readable
  stderr: Readable
  exitCode: Promise<number>

  pipe(dest): ProcessPromise

  kill(): Promise<void>

  nothrow(): this

  quiet(): this
}

Read more about the ProcessPromise.

class ProcessOutput {
  readonly stdout: string
  readonly stderr: string
  readonly signal: string
  readonly exitCode: number

  toString(): string // Combined stdout & stderr.
}

The output of the process is captured as-is. Usually, programs print a new line \n at the end. If ProcessOutput is used as an argument to some other $ process, zx will use stdout and trim the new line.

let date = await $`date`
await $`echo Current date is ${date}.`

Changes the current working directory.

cd('/tmp')
await $`pwd` // => /tmp

A wrapper around the node-fetch package.

let resp = await fetch('https://medv.io')

A wrapper around the readline package.

let bear = await question('What kind of bear is best? ')

A wrapper around the setTimeout function.

await sleep(1000)

A console.log() alternative which can take ProcessOutput.

let branch = await $`git branch --show-current`

echo`Current branch is ${branch}.`
// or
echo('Current branch is', branch)

Returns the stdin as a string.

let content = JSON.parse(await stdin())

Creates a new async context.

await $`pwd` // => /home/path

within(async () => {
  cd('/tmp')

  setTimeout(async () => {
    await $`pwd` // => /tmp
  }, 1000)
})

await $`pwd` // => /home/path

let version = await within(async () => {
  $.prefix += 'export NVM_DIR=$HOME/.nvm; source $NVM_DIR/nvm.sh; '
  await $`nvm use 16`
  return $`node -v`
})

Retries a callback for a few times. Will return after the first successful attempt, or will throw after specifies attempts count.

let p = await retry(10, () => $`curl https://medv.io`)

// With a specified delay between attempts.
let p = await retry(20, '1s', () => $`curl https://medv.io`)

// With an exponential backoff.
let p = await retry(30, expBackoff(), () => $`curl https://medv.io`)

Starts a simple CLI spinner.

await spinner(() => $`long-running command`)

// With a message.
await spinner('working...', () => $`sleep 99`)

The following packages are available without importing inside scripts.

The chalk package.

console.log(chalk.blue('Hello world!'))

The fs-extra package.

let {version} = await fs.readJson('./package.json')

The os package.

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

The path package.

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

The globby package.

let packages = await glob(['package.json', 'packages/*/package.json'])

The yaml package.

console.log(YAML.parse('foo: bar').foo)

The minimist package available as global const argv.

if (argv.someFlag) {
  echo('yes')
}

The which package.

let node = await which('node')

Specifies what shell is used. Default is which bash.

$.shell = '/usr/bin/bash'

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

Specifies a spawn api. Defaults to require('child_process').spawn.

Specifies the command that will be prefixed to all commands run.

Default is set -euo pipefail;.

Or use a CLI argument: --prefix='set -e;'

Specifies a function for escaping special characters during command substitution.

Specifies verbosity. Default is true.

In verbose mode, zx prints all executed commands alongside with their outputs.

Or use the CLI argument --quiet to set $.verbose = false.

Specifies an environment variables map.

Defaults to process.env.

Specifies a current working directory of all processes created with the $.

The cd() func changes only process.cwd() and if no $.cwd specified, all $ processes use process.cwd() by default (same as spawn behavior).

Specifies a logging function.

import { LogEntry, log } from 'zx/core'

$.log = (entry: LogEntry) => {
  switch (entry.kind) {
    case 'cmd':
      // for example, apply custom data masker for cmd printing
      process.stderr.write(masker(entry.cmd))
      break
    default:
      log(entry)
  }
}

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).

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')

process.env.FOO = 'bar'
await $`echo $FOO`

When passing an array of values as an argument to $, items of the array will be escaped individually and concatenated via space.

Example:

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

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

#!/usr/bin/env node
import { $ } from 'zx'

await $`date`

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

The zx can execute scripts written as markdown:

zx docs/markdown.md

import { $ } from 'zx'
// Or
import 'zx/globals'

void async function () {
  await $`ls -la`
}()

Set "type": "module" in package.json and "module": "ESNext" in tsconfig.json.

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

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

The zx supports executing scripts from stdin.

zx << 'EOF'
await $`pwd`
EOF

Evaluate the following argument as a script.

cat package.json | zx --eval 'let v = JSON.parse(await stdin()).version; echo(v)'

// script.mjs:
import sh from 'tinysh'

sh.say('Hello, world!')

Add --install flag to the zx command to install missing dependencies automatically.

zx --install script.mjs

You can also specify needed version by adding comment with @ after the import.

import sh from 'tinysh' // @^1

The zx uses webpod to execute commands on remote hosts.

import { ssh } from 'zx'

await ssh('user@host')`echo Hello, world!`

By default child_process does not include aliases and bash functions. But you are still able to do it by hand. Just attach necessary directives to the $.prefix.

$.prefix += 'export NVM_DIR=$HOME/.nvm; source $NVM_DIR/nvm.sh; '
await $`nvm -v`

The default GitHub Action runner comes with npx installed.

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3

      - name: Build
        env:
          FORCE_COLOR: 3
        run: |
          npx zx <<'EOF'
          await $`...`
          EOF

Impatient early adopters can try the experimental zx versions. But keep in mind: these builds are ⚠️️__beta__ in every sense.

npm i zx@dev
npx zx@dev --install --quiet <<< 'import _ from "lodash" /* 4.17.15 */; console.log(_.VERSION)'

Apache-2.0

Disclaimer: This is not an officially supported Google product.