Node js linux command

Node.js v20.4.0 documentation

Please see the Command-line options document for more information.

Example #

An example of a web server written with Node.js which responds with ‘Hello, World!’ :

Commands in this document start with $ or > to replicate how they would appear in a user’s terminal. Do not include the $ and > characters. They are there to show the start of each command.

Lines that don’t start with $ or > character show the output of the previous command.

First, make sure to have downloaded and installed Node.js. See Installing Node.js via package manager for further install information.

Now, create an empty project folder called projects , then navigate into it.

mkdir ~/projects cd ~/projects copy

mkdir %USERPROFILE%\projects cd %USERPROFILE%\projects copy

mkdir $env:USERPROFILE\projects cd $env:USERPROFILE\projects copy

Next, create a new source file in the projects folder and call it hello-world.js .

Open hello-world.js in any preferred text editor and paste in the following content:

const http = require('node:http'); const hostname = '127.0.0.1'; const port = 3000; const server = http.createServer((req, res) => < res.statusCode = 200; res.setHeader('Content-Type', 'text/plain'); res.end('Hello, World!\n'); >); server.listen(port, hostname, () => < console.log(`Server running at http://$ :$ /`); >); copy

Save the file, go back to the terminal window, and enter the following command:

Output like this should appear in the terminal:

Server running at http://127.0.0.1:3000/ copy

Now, open any preferred web browser and visit http://127.0.0.1:3000 .

If the browser displays the string Hello, World! , that indicates the server is working.

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How to Execute Shell Commands With Node.Js

This tutorial will teach you how to execute shell commands, and even your own custom shell scripts with Node.js.

We will learn how to create a program in Node.js to run common commands like ls , mkdir or even npm on your Unix system (Mac or Linux).

If you just want to see the code, you can view it on Github

The Child Process Module#

When we execute shell commands, we are running code outside of our Node.js application. In order to do this, we need to run these commands in a child process.

A child process is code that is run in a different thread (and process id) outside your Node.js application. However, we can still send and receive information from the child process using standard I/O streams.

In Node.js, we can use the child_process standard library to start these processes to run shell commands.

Running Basic Shell Commands#

To run a simple command and read its output, we can use the exec function.

In this example, let’s list the files in our current directory using ls , and print the output from our Node.js code:

const < exec > = require('node:child_process')  // run the `ls` command using exec  exec('ls ./', (err, output) =>   // once the command has completed, the callback function is called  if (err)   // log and return if we encounter an error  console.error("could not execute command: ", err)  return  >  // log the output received from the command  console.log("Output: \n", output) >) 

Since I am running this code within the example repository, it prints the files in the project root:

Output: LICENSE README.md index.js package.json 

Note that when we run exec, our application spawns a shell ( ‘/bin/sh’ by default) and runs the given command on that shell. This means that the command is first processed by the shell and then executed.

So for example, when we run ls ./*.md , the shell processes ./*.md into README.md and then runs the command ls README.md :

We are also limited to 1MB by default as the maximum size of output generated by the command.

Executing Long Running Commands#

The previous example executed the ls command that returned its output immediately. What about commands whose output is continuous, or takes a long time to retrieve?

For example, when we run the ping command, we get continuous output at periodic intervals:

➜ ~ ping google.com PING google.com (142.250.77.110): 56 data bytes 64 bytes from 142.250.77.110: icmp_seq=0 ttl=116 time=11.397 ms 64 bytes from 142.250.77.110: icmp_seq=1 ttl=116 time=17.646 ms ## this is received after 1 second 64 bytes from 142.250.77.110: icmp_seq=2 ttl=116 time=10.036 ms ## this is received after 2 seconds 64 bytes from 142.250.77.110: icmp_seq=3 ttl=116 time=9.656 ms ## and so on # . 

If we tried executing this type of command using exec , we are limited by the maximum output constraint. Additionally, the exec function callback waits for the command to complete and returns the output after that.

Instead, we can use the spawn function to read output continuously, and without limit:

const < spawn > = require('node:child_process')  // start the `ping google.com` command  const command = spawn('ping', ["google.com"])  // the `data` event is fired every time data is // output from the command  command.stdout.on('data', output =>   // the output data is captured and printed in the callback  console.log("Output: ", output.toString()) >) 

Output: PING google.com (142.250.77.110): 56 data bytes 64 bytes from 142.250.77.110: icmp_seq=0 ttl=116 time=9.550 ms Output: 64 bytes from 142.250.77.110: icmp_seq=1 ttl=116 time=17.892 ms Output: 64 bytes from 142.250.77.110: icmp_seq=2 ttl=116 time=9.466 ms Output: 64 bytes from 142.250.77.110: icmp_seq=3 ttl=116 time=18.592 ms Output: 64 bytes from 142.250.77.110: icmp_seq=4 ttl=116 time=9.712 ms 

By taking an event driven approach, we can capture the output throughout the commands lifecycle, and process it as soon as it is received.

Note that unlike exec , the spawn function does not create a new shell to process the command, and executes it directly.

Another example of a long-running command is npm install — which gives continuous output during the module installation process. In this case as well, it makes sense to give the user continuous feedback as soon as output is received

Passing Input To Commands With STDIN#

In the previous examples, we executed commands without giving any input (or providing limited inputs as arguments). In most cases, input is given through the STDIN stream.

One popular example of this is the grep command, where we can pipe the input from another command:

➜ ~ echo "1. pear\n2. grapes\n3. apple\n4. banana\n" | grep apple 3. apple 

Here, the input is passed to the grep command through STDIN. In this case the input is a list of fruit, and grep filters the line that contains «apple»

The child process object returned by the spawn function provides us with an input stream which we can write into. Let’s use it to pass input to a grep child process:

const < spawn > = require('node:child_process')  // run the grep command  const command = spawn('grep', ["apple"])  // use the stdin stream from the command to // send data to the spawned command  command.stdin.write("1. pear\n") command.stdin.write("2. grapes\n") command.stdin.write("3. apple\n") command.stdin.write("4. banana\n") // once we're done sending input, call the `end` method  command.stdin.end()  // similar to the previous example, print the output whenever it's // received  command.stdout.on('data', output =>   console.log("Output: ", output.toString()) >) 

Killing a Child Process#

There are several commands that run indefinitely, or need an explicit signal to stop.

For example, if we start a web server using python3 -m http.server or execute sleep 10000 the resulting child processes will run for a very long time (or indefinitely).

To stop these processes, we need to send a kill signal from our Node.js application. We can do this using the kill method of any child process object.

const < exec > = require('node:child_process')  // execute the sleep command - this will // wait for 100 seconds before exiting  const command = exec("sleep 100")  // when a child process exits, it fires // the "close" event  command.on('close', (code) =>   console.log('process has exited') >)  // Since we don't want to wait for 100 seconds, // we can send a kill command after a 1 second timeout  setTimeout(() =>   command.kill() >, 1000) 

This will give the following output after 1 second has elapsed:

Terminating child processes is useful when you want to limit the time spent in running a command or want to create a fallback incase a command doesn’t return a result on time.

Conclusion#

• Use exec when you want to execute simple commands that don’t usually give too much output
• For functions with continuous or long-running output, you should use spawn instead. However, note that you won’t get any of the shell processing (like wildcards or command chaining) that you would get with exec
• In production applications, its useful to keep a timeout and kill a process if it isn’t responding for a given time. We can send termination commands using the kill method to achieve this

If you want to read more about the different functions and configuration options, you can view the official documentation page.

You can view the working code for all examples on Github.

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Полезные команды для работы с Node.js

Перед тем как рассматривать полезные команды при работе с Node.js, её необходимо установить.

Команды помогают узнать версию Node.js,

node -h — показывает список всех доступных команд Node.js.

node -v , node —version — показывает установленную версию Node.js.

npm -h — показывает список всех доступных команд пакетного менеджера npm .

npm -v , npm —version — показывает установленную версию npm .

Команда npm update npm -g позволяет обновить версию npm .

npm list —depth=0 показывает список установленных пакетов.

Команда npm outdated —depth=0 покажет список установленных пакетов, которые требуют обновления. Если все пакеты обновлены, список будет пустым.

npm install package — позволяет установить любой пакет по его имени. Если при этом к команде добавить префикс -g пакет будет установлен глобально на весь компьютер.

Команда npm i package является укороченной альтернативой предыдущей команды.

Если вы хотите установить конкретную версию пакета, воспользуйтесь префиксом @ с номером версии. Например, npm install package@1.0.1 .

npm uninstall package — удаляет установленный пакет по имени.

Команда npm list package — покажет версию установленного пакета, а команда npm view package version — последнюю версию пакета, которая существует.

Для работы с пакетным менеджером также пригодится файл package.json , который должен лежать в директории, с которой происходит работа в консоли.

Он содержит различные мета-данные, например, имя проекта, версия, описания и автор. Также он содержит список зависимостей, которые будут установлены, если вызвать из этой папки команду npm install .

Кроме этого он ещё имеет скрипты, которые вызывают другие команды консоли. Например, для этого файла вызов команды npm start вызовет запуск задачи Grunt с именем dev . А команда npm run build вызовет скрипт build , который запустит задачу в Grunt с именем build .

Во время работы часто возникает необходимость установить некоторые пакеты. Если установить пакет с префиксом —save , то он автоматически запишется в package.json в раздел dependencies . Такая же команда с префиксом —save-dev запишет пакет в раздел devDependencies .

nvm (илиNode Version Manager) — утилита, которая позволяет быстро менять версии Node.js.

Чтобы её установить, достаточно запустить скрипт

curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.31.0/install.sh | bash 

Теперь можно установить последнюю версию Node.js, например, 5.0 с помощью команды nvm install 5.0 . Чтобы начать использовать её, введите команду nvm use 5.0 . Таким образом, можно быстро переключаться между версиями, например, для тестирования.

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