🐚 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 version >= 16.0.0

Goods

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

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.

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

import 'zx/globals'

$`command`

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}`)
}

ProcessPromise

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.

ProcessOutput

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}.`

Functions

cd()

Changes the current working directory.

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

fetch()

A wrapper around the node-fetch package.

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

question()

A wrapper around the readline package.

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

sleep()

A wrapper around the setTimeout function.

await sleep(1000)

echo()

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)

stdin()

Returns the stdin as a string.

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

within()

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`
})

Packages

Following packages are available without importing inside scripts.

chalk package

The chalk package.

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

fs package

The fs-extra package.

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

os package

The os package.

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

path package

The path package.

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

globby package

The globby package.

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

yaml package

The yaml package.

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

minimist package

The minimist package available as global const argv.

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

which package

The which package.

let node = await which('node')

Configuration

$.shell

Specifies what shell is used. Default is which bash.

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

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

$.spawn

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

$.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.

$.env

Specifies an environment variables map.

Defaults to process.env.

$.cwd

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).

$.log

Specifies a logging function.

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')

Experimental

The zx also provides a few experimental functions. Please leave a feedback about those features in the discussion. To enable new features via CLI pass --experimental flag.

retry()

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

import { retry, expBackoff } from 'zx/experimental'

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`)

spinner()

Starts a simple CLI spinner.

import { spinner } from 'zx/experimental'

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

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

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

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.

Executing remote scripts

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

Executing scripts from stdin

The zx supports executing scripts from stdin.

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

Executing scripts via --eval

Evaluate the following argument as a script.

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

Attaching a profile

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 $.prefix.

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

Using GitHub Actions

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

License

Apache-2.0

Disclaimer: This is not an officially supported Google product.