Process execution for humans
Execa runs commands in your script, application or library. Unlike shells, it is optimized for programmatic usage. Built on top of the child_process core module.
One of the maintainers @ehmicky is looking for a remote full-time position. Specialized in Node.js back-ends and CLIs, he led Netlify Build, Plugins and Configuration for 2.5 years. Feel free to contact him on his website or on LinkedIn!
Features
- Simple syntax: promises and template strings, like
zx. - Script interface.
- No escaping nor quoting needed. No risk of shell injection.
- Execute locally installed binaries without
npx. - Improved Windows support: shebangs,
PATHEXT, and more. - Detailed errors and verbose mode, for debugging.
- Pipe multiple subprocesses better than in shells: retrieve intermediate results, use multiple sources/destinations, unpipe.
- Split the output into text lines, or iterate progressively over them.
- Strip unnecessary newlines.
- Get interleaved output from
stdoutandstderrsimilar to what is printed on the terminal. - Retrieve the output programmatically and print it on the console at the same time.
- Transform or filter the input and output with simple functions.
- Redirect the input and output from/to files, strings,
Uint8Arrays, iterables or objects. - Pass Node.js streams or web streams to subprocesses, or convert subprocesses to a stream.
- Ensure subprocesses exit even when they intercept termination signals, or when the current process ends abruptly.
Install
npm install execaDocumentation
Execution:
▶️ Basic execution- 💬 Escaping/quoting
- 💻 Shell
- 📜 Scripts
- 🐢 Node.js files
- 🌐 Environment
- ❌ Errors
- 🏁 Termination
Input/output:
- 🎹 Input
- 📢 Output
- 📃 Text lines
- 🤖 Binary data
- 🧙 Transforms
Advanced usage:
- 🔀 Piping multiple subprocesses
- ⏳️ Streams
- 📞 Inter-process communication
- 🐛 Debugging
- 📎 Windows
- 🔍 Difference with Bash and zx
- 🤓 TypeScript
- 📔 API reference
Examples
Execution
Simple syntax
import {execa} from 'execa';
const {stdout} = await execa`npm run build`;
// Print command's output
console.log(stdout);Script
import {$} from 'execa';
const {stdout: name} = await $`cat package.json`.pipe`grep name`;
console.log(name);
const branch = await $`git branch --show-current`;
await $`dep deploy --branch=${branch}`;
await Promise.all([
$`sleep 1`,
$`sleep 2`,
$`sleep 3`,
]);
const directoryName = 'foo bar';
await $`mkdir /tmp/${directoryName}`;Local binaries
$ npm install -D eslintawait execa({preferLocal: true})`eslint`;Pipe multiple subprocesses
const {stdout, pipedFrom} = await execa`npm run build`
.pipe`sort`
.pipe`head -n 2`;
// Output of `npm run build | sort | head -n 2`
console.log(stdout);
// Output of `npm run build | sort`
console.log(pipedFrom[0].stdout);
// Output of `npm run build`
console.log(pipedFrom[0].pipedFrom[0].stdout);Input/output
Interleaved output
const {all} = await execa({all: true})`npm run build`;
// stdout + stderr, interleaved
console.log(all);Programmatic + terminal output
const {stdout} = await execa({stdout: ['pipe', 'inherit']})`npm run build`;
// stdout is also printed to the terminal
console.log(stdout);Files
// Similar to: npm run build > output.txt
await execa({stdout: {file: './output.txt'}})`npm run build`;Simple input
const {stdout} = await execa({input: getInputString()})`sort`;
console.log(stdout);Split into text lines
const {stdout} = await execa({lines: true})`npm run build`;
// Print first 10 lines
console.log(stdout.slice(0, 10).join('\n'));Streaming
Iterate over text lines
for await (const line of execa`npm run build`) {
if (line.includes('WARN')) {
console.warn(line);
}
}Transform/filter output
let count = 0;
// Filter out secret lines, then prepend the line number
const transform = function * (line) {
if (!line.includes('secret')) {
yield `[${count++}] ${line}`;
}
};
await execa({stdout: transform})`npm run build`;Web streams
const response = await fetch('https://example.com');
await execa({stdin: response.body})`sort`;Convert to Duplex stream
import {execa} from 'execa';
import {pipeline} from 'node:stream/promises';
import {createReadStream, createWriteStream} from 'node:fs';
await pipeline(
createReadStream('./input.txt'),
execa`node ./transform.js`.duplex(),
createWriteStream('./output.txt'),
);Debugging
Detailed error
import {execa, ExecaError} from 'execa';
try {
await execa`unknown command`;
} catch (error) {
if (error instanceof ExecaError) {
console.log(error);
}
/*
ExecaError: Command failed with ENOENT: unknown command
spawn unknown ENOENT
at ...
at ... {
shortMessage: 'Command failed with ENOENT: unknown command\nspawn unknown ENOENT',
originalMessage: 'spawn unknown ENOENT',
command: 'unknown command',
escapedCommand: 'unknown command',
cwd: '/path/to/cwd',
durationMs: 28.217566,
failed: true,
timedOut: false,
isCanceled: false,
isTerminated: false,
isMaxBuffer: false,
code: 'ENOENT',
stdout: '',
stderr: '',
stdio: [undefined, '', ''],
pipedFrom: []
[cause]: Error: spawn unknown ENOENT
at ...
at ... {
errno: -2,
code: 'ENOENT',
syscall: 'spawn unknown',
path: 'unknown',
spawnargs: [ 'command' ]
}
}
*/
}Verbose mode
await execa`npm run build`;
await execa`npm run test`;
Related
- gulp-execa - Gulp plugin for Execa
- nvexeca - Run Execa using any Node.js version