trevorlazarus / zx

A tool for writing better scripts

🐚 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

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

When using zx via the executable or a shebang, all of the functions ($, cd, fetch, etc) are available straight away without any imports.

$`command`

Executes a given string using the exec function from the child_process package and returns Promise<ProcessOutput>.

let count = parseInt(await $`ls -1 | wc -l`)
console.log(`Files count: ${count}`)

For example, to upload files in parallel:

let hosts = [...]
await Promise.all(hosts.map(host =>
  $`rsync -azP ./src ${host}:/var/www`  
))

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}`)
}

ProcessOutput

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

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.

type QuestionOptions = { choices: string[] }

function question(query?: string, options?: QuestionOptions): Promise<string>

Usage:

let username = await question('What is your username? ')
let token = await question('Choose env variable: ', {
  choices: Object.keys(process.env)
})

sleep()

A wrapper around the setTimeout function.

function sleep(ms: number): Promise<void>

Usage:

await sleep(1000)

chalk package

The chalk package is available without importing inside scripts.

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

fs package

The fs package is available without importing inside scripts. It is asynchronous by default.

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

os package

The os package is available without importing inside scripts.

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

$.shell

Specifies what shell is used. Default is which bash.

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

$.prefix

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

Default is set -euo pipefail;.

$.quote

Specifies a function what will be used for escaping special characters during command substitution.

Default is the shq package.

$.verbose

Specifies verbosity. Default is true.

In verbose mode, the zx prints all executed commands alongside with their outputs. This is the same as using set -x in Bash.

__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')

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`

Passing env variables

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

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

License

Apache-2.0

Disclaimer: This is not an officially supported Google product.