# Concurrently — Run Multiple Commands in Parallel from One Terminal

> A CLI utility that runs multiple commands concurrently with prefixed, color-coded output in a single terminal window. Commonly used in package.json scripts to start a dev server and a file watcher side by side.

## Install

Save in your project root:

# Concurrently — Run Multiple Commands in Parallel from One Terminal

## Quick Use
```bash
npx concurrently "npm:dev" "npm:watch"
# Or with custom labels
npx concurrently -n server,build "node server.js" "webpack --watch"
```

## Introduction
Concurrently is a Node.js CLI tool that runs multiple commands simultaneously in a single terminal session. It color-codes and prefixes each command's output so you can distinguish between processes at a glance. It is widely used in `package.json` scripts to start frontend and backend servers, file watchers, and build processes together.

## What Concurrently Does
- Launches multiple shell commands in parallel from a single invocation
- Prefixes each command's stdout and stderr with a customizable name and color
- Supports npm script shorthand (`npm:dev`, `npm:build`) to run package.json scripts by name
- Kills all running processes when one exits, or keeps the rest alive based on configuration
- Returns a combined exit code based on configurable success/failure conditions

## Architecture Overview
Concurrently spawns child processes using Node.js's `child_process.spawn` for each command. Each process's stdout and stderr streams are piped through a transform that prepends a colored prefix. A controller monitors process lifecycle events and applies the configured kill/restart policy. The tool supports running commands from `package.json` by resolving script names via npm's internal script runner.

## Self-Hosting & Configuration
- Install as a dev dependency with `npm install -D concurrently` or run ad-hoc with `npx`
- Use `-n` to assign custom names and `-c` to assign specific colors to each command
- Set `--kill-others` to terminate all commands if any one exits
- Set `--kill-others-on-fail` to only kill siblings when a command exits with a non-zero code
- Use `--prefix-colors` with ANSI color names or hex codes for custom styling

## Key Features
- Color-coded, prefixed output makes it easy to identify which process produced each log line
- npm script shorthand (`npm:*` wildcards) runs matching package.json scripts without repeating `npm run`
- Configurable kill and restart policies for managing dependent processes
- Works on Linux, macOS, and Windows including Git Bash and PowerShell
- Lightweight with no native dependencies

## Comparison with Similar Tools
- **npm-run-all** — runs npm scripts sequentially or in parallel; concurrently offers richer output formatting and process control
- **GNU Parallel** — powerful parallel command executor for shell; heavier and not designed for npm script workflows
- **Mprocs** — TUI-based process manager with split panes; concurrently uses a single merged output stream
- **Foreman / Overmind** — Procfile-based process managers; concurrently is simpler and works inline in npm scripts

## FAQ
**Q: Can I restart a command if it crashes?**
A: Yes, use the `--restart-tries` and `--restart-after` flags to configure automatic restart behavior for failing commands.

**Q: How do I run all npm scripts matching a pattern?**
A: Use the `npm:*` wildcard syntax, for example `concurrently "npm:watch-*"` runs all scripts whose names start with `watch-`.

**Q: Does concurrently work on Windows?**
A: Yes, it supports Windows natively including cmd.exe, PowerShell, and Git Bash.

**Q: How do I control the exit code?**
A: Use `--success` to define which command's exit code determines the overall result: `first`, `last`, `all`, or a specific command index.

## Sources
- https://github.com/open-cli-tools/concurrently
- https://www.npmjs.com/package/concurrently

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Source: https://tokrepo.com/en/workflows/asset-540bfd80
Author: AI Open Source