concurrently

What is concurrently?

The 'concurrently' npm package is a utility that allows you to run multiple commands concurrently. It is often used to run multiple processes during development, such as a server and a client application at the same time. It can handle the output of these processes, terminate them all together, and more.

What are concurrently's main functionalities?

Running multiple commands

This feature allows you to run multiple commands at the same time. Each command is quoted and separated by a space.

concurrently "command1 arg" "command2 arg"

Customizing the prefix for command output

This feature allows you to customize the prefix shown in the output for each command. In this example, 'API' and 'UI' are custom prefixes for the two npm scripts.

concurrently --names "API,UI" "npm:api" "npm:start"

Killing all commands when one of them exits

This feature ensures that if one command exits, all other commands are also terminated. This is useful for cleaning up processes if one fails.

concurrently --kill-others "command1" "command2"

Running commands sequentially

This feature allows you to run commands sequentially instead of concurrently. The --success option determines which command's exit code will be used as the exit code for concurrently.

concurrently "command1" "command2" --success first

Other packages similar to concurrently

npm-run-all

A CLI tool to run multiple npm-scripts in parallel or sequential. It is similar to concurrently but specifically designed for npm scripts. It provides a simpler interface for running scripts in series or parallel.

pm2

PM2 is a production process manager for Node.js applications with a built-in load balancer. It is more feature-rich than concurrently, providing a daemon process that helps keep applications alive forever, facilitates common system admin tasks, and can be used in production environments.

foreman

Foreman is a manager for Procfile-based applications. Its focus is on easing the development of applications by allowing you to run multiple processes with a single command. It is not limited to Node.js and can be used with any language or markup.

README

Concurrently

Run multiple commands concurrently. Like npm run watch-js & npm run watch-less but better.

Table of contents

• Concurrently
  • Why
  • Install
  • Usage
  • Programmatic Usage
    • concurrently(commands[, options])
  • FAQ

Why

I like task automation with npm but the usual way to run multiple commands concurrently is npm run watch-js & npm run watch-css. That's fine but it's hard to keep on track of different outputs. Also if one process fails, others still keep running and you won't even notice the difference.

Another option would be to just run all commands in separate terminals. I got tired of opening terminals and made concurrently.

Features:

• Cross platform (including Windows)
• Output is easy to follow with prefixes
• With --kill-others switch, all commands are killed if one dies
• Spawns commands with spawn-command

Install

The tool is written in Node.js, but you can use it to run any commands.

npm install -g concurrently

or if you are using it from npm scripts:

npm install concurrently --save

Usage

Remember to surround separate commands with quotes:

concurrently "command1 arg" "command2 arg"

Otherwise concurrently would try to run 4 separate commands: command1, arg, command2, arg.

In package.json, escape quotes:

"start": "concurrently \"command1 arg\" \"command2 arg\""

NPM run commands can be shortened:

concurrently "npm:watch-js" "npm:watch-css" "npm:watch-node"

# Equivalent to:
concurrently -n watch-js,watch-css,watch-node "npm run watch-js" "npm run watch-css" "npm run watch-node"

NPM shortened commands also support wildcards. Given the following scripts in package.json:

{
    //...
    "scripts": {
        // ...
        "watch-js": "...",
        "watch-css": "...",
        "watch-node": "...",
        // ...
    },
    // ...
}

concurrently "npm:watch-*"

# Equivalent to:
concurrently -n js,css,node "npm run watch-js" "npm run watch-css" "npm run watch-node"

# Any name provided for the wildcard command will be used as a prefix to the wildcard
# part of the script name:
concurrently -n w: npm:watch-*

# Equivalent to:
concurrently -n w:js,w:css,w:node "npm run watch-js" "npm run watch-css" "npm run watch-node"

Good frontend one-liner example here.

Help:

concurrently [options] <command ...>

General
  -m, --max-processes  How many processes should run at once.
                       New processes only spawn after all restart tries of a
                       process.                                         [number]
  -n, --names          List of custom names to be used in prefix template.
                       Example names: "main,browser,server"             [string]
  --name-separator     The character to split <names> on. Example usage:
                       concurrently -n "styles|scripts|server" --name-separator
                       "|"                                        [default: ","]
  -r, --raw            Output only raw output of processes, disables prettifying
                       and concurrently coloring.                      [boolean]
  -s, --success        Return exit code of zero or one based on the success or
                       failure of the "first" child to terminate, the "last
                       child", or succeed only if "all" child processes succeed.
                              [choices: "first", "last", "all"] [default: "all"]
  --no-color           Disables colors from logging                    [boolean]

Prefix styling
  -p, --prefix            Prefix used in logging for each process.
                          Possible values: index, pid, time, command, name,
                          none, or a template. Example template: "{time}-{pid}"
                         [string] [default: index or name (when --names is set)]
  -c, --prefix-colors     Comma-separated list of chalk colors to use on
                          prefixes. If there are more commands than colors, the
                          last color will be repeated.
                          - Available modifiers: reset, bold, dim, italic,
                          underline, inverse, hidden, strikethrough
                          - Available colors: black, red, green, yellow, blue,
                          magenta, cyan, white, gray, or any hex values for
                          colors, eg #23de43
                          - Available background colors: bgBlack, bgRed,
                          bgGreen, bgYellow, bgBlue, bgMagenta, bgCyan, bgWhite
                          See https://www.npmjs.com/package/chalk for more
                          information.            [string] [default: "reset"]
  -l, --prefix-length     Limit how many characters of the command is displayed
                          in prefix. The option can be used to shorten the
                          prefix when it is set to "command"
                                                          [number] [default: 10]
  -t, --timestamp-format  Specify the timestamp in moment/date-fns format.
                                   [string] [default: "yyyy-MM-dd HH:mm:ss.SSS"]

Input handling
  -i, --handle-input      Whether input should be forwarded to the child
                          processes. See examples for more information.[boolean]
  --default-input-target  Identifier for child process to which input on stdin
                          should be sent if not specified at start of input.
                          Can be either the index or the name of the process.
                                                                    [default: 0]

Killing other processes
  -k, --kill-others      kill other processes if one exits or dies     [boolean]
  --kill-others-on-fail  kill other processes if one exits with non zero status
                         code                                          [boolean]

Restarting
      --restart-tries  How many times a process that died should restart.
                       Negative numbers will make the process restart forever.
                                                           [number] [default: 0]
      --restart-after  Delay time to respawn the process, in milliseconds.
                                                           [number] [default: 0]

Options:
  -h, --help         Show help                                         [boolean]
  -v, -V, --version  Show version number                               [boolean]

Examples:

 - Output nothing more than stdout+stderr of child processes

     $ concurrently --raw "npm run watch-less" "npm run watch-js"

 - Normal output but without colors e.g. when logging to file

     $ concurrently --no-color "grunt watch" "http-server" > log

 - Custom prefix

     $ concurrently --prefix "{time}-{pid}" "npm run watch" "http-server"

 - Custom names and colored prefixes

     $ concurrently --names "HTTP,WATCH" -c "bgBlue.bold,bgMagenta.bold"
     "http-server" "npm run watch"

 - Send input to default

     $ concurrently --handle-input "nodemon" "npm run watch-js"
     rs  # Sends rs command to nodemon process

 - Send input to specific child identified by index

     $ concurrently --handle-input "npm run watch-js" nodemon
     1:rs

 - Send input to specific child identified by name

     $ concurrently --handle-input -n js,srv "npm run watch-js" nodemon
     srv:rs

 - Shortened NPM run commands

     $ concurrently npm:watch-node npm:watch-js npm:watch-css

 - Shortened NPM run command with wildcard

     $ concurrently npm:watch-*

For more details, visit https://github.com/open-cli-tools/concurrently

Programmatic Usage

concurrently can be used programmatically by using the API documented below:

concurrently(commands[, options])

• commands: an array of either strings (containing the commands to run) or objects with the shape { command, name, prefixColor, env, cwd }.

• options (optional): an object containing any of the below:

  • cwd: the working directory to be used by all commands. Can be overriden per command. Default: process.cwd().
  • defaultInputTarget: the default input target when reading from inputStream. Default: 0.
  • handleInput: when true, reads input from process.stdin.
  • inputStream: a Readable stream to read the input from. Should only be used in the rare instance you would like to stream anything other than process.stdin. Overrides handleInput.
  • pauseInputStreamOnFinish: by default, pauses the input stream (process.stdin when handleInput is enabled, or inputStream if provided) when all of the processes have finished. If you need to read from the input stream after concurrently has finished, set this to false. (#252).
  • killOthers: an array of exitting conditions that will cause a process to kill others. Can contain any of success or failure.
  • maxProcesses: how many processes should run at once.
  • outputStream: a Writable stream to write logs to. Default: process.stdout.
  • prefix: the prefix type to use when logging processes output. Possible values: index, pid, time, command, name, none, or a template (eg [{time} process: {pid}]). Default: the name of the process, or its index if no name is set.
  • prefixLength: how many characters to show when prefixing with command. Default: 10
  • raw: whether raw mode should be used, meaning strictly process output will be logged, without any prefixes, colouring or extra stuff.
  • successCondition: the condition to consider the run was successful. If first, only the first process to exit will make up the success of the run; if last, the last process that exits will determine whether the run succeeds. Anything else means all processes should exit successfully.
  • restartTries: how many attempts to restart a process that dies will be made. Default: 0.
  • restartDelay: how many milliseconds to wait between process restarts. Default: 0.
  • timestampFormat: a date-fns format to use when prefixing with time. Default: yyyy-MM-dd HH:mm:ss.ZZZ

Returns: a Promise that resolves if the run was successful (according to successCondition option), or rejects, containing an array of objects with information for each command that has been run, in the order that the commands terminated. The objects have the shape { command, index, exitCode, killed }, where command is the object passed in the commands array, index its index there and killed indicates if the process was killed as a result of killOthers. Default values (empty strings or objects) are returned for the fields that were not specified.

Example:

const concurrently = require('concurrently');
concurrently([
    'npm:watch-*',
    { command: 'nodemon', name: 'server' },
    { command: 'deploy', name: 'deploy', env: { PUBLIC_KEY: '...' } },
    { command: 'watch', name: 'watch', cwd: path.resolve(__dirname, 'scripts/watchers')}
], {
    prefix: 'name',
    killOthers: ['failure', 'success'],
    restartTries: 3,
    cwd: path.resolve(__dirname, 'scripts'),
}).then(success, failure);

FAQ

• Process exited with code null?

  From Node child_process documentation, exit event:

  This event is emitted after the child process ends. If the process terminated normally, code is the final exit code of the process, otherwise null. If the process terminated due to receipt of a signal, signal is the string name of the signal, otherwise null.

  So null means the process didn't terminate normally. This will make concurrent to return non-zero exit code too.

• Does this work with the npm-replacements yarn or pnpm?

  Yes! In all examples above, you may replace "npm" with "yarn" or "pnpm".