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Bash scripting

Links

Create a file

How to run a script

Run a script during boot

Reverse Proxy

Create a file

  • Create a file called "filename".sh
    • touch provision.sh
  • Change permission of the file
    • chmod +x provision.sh
  • first line MUST start with #!/bin/bash

File code

We want to create a file that does everything in the bullet points below.

  • update & upgrade
  • installed nginx
  • start nginx
  • enable nginx
  • stopped then started
#!/bin/bash

# update
sudo apt-get update -y

# upgrade
sudo apt-get upgrade -y

# install nginx
sudo apt-get install nginx -y

# start nginx
sudo systemctl start nginx

# enable nginx
sudo systemctl enable nginx

We need to add #!/bin/bash at the start of every bash script for the terminal to recognize it as a script.

We also need to add -y so that when the script runs, we don't haave to ask for permission from the user.

How to run a script

The way to run a bash script is to find the file path

sudo ./provision.sh

This would run a bash script called provision, and this would be in your directory you are in.

Run a script during boot time

The way to run a script during the boot of the vm. You need to create a bash script within your localhost.

In our provision.sh

#!/bin/bash

#update & upgrade
sudo apt-get update -y

sudo apt-get upgrade -y

# install nginx
sudo apt-get install nginx -y

# start nginx
sudo systemctl start nginx

# enable nginx
sudo systemctl enable nginx

You go into the Vagrantfile and add it in (You need to remember the file location as it can be relative or absolute)

File within the same folder as the Vagrantfile

 # Adding a external script so that script executes with boot time
  config.vm.provision "shell", path: "./provision.sh", run: "always"

If you want to upload a file or folder

  config.vm.provision "file", source: "./file.sh", destination: "file.sh", run: "always"

The run: "always" command makes sure that the script is run, no matter what.

Syncing folders and files to the VM

To sync folders to the vm, you add the code below to your Vagrantfile

  config.vm.synced_folder ".", "/home/vagrant/app"

This will sync all the files and folders in your current dir as . means all files and folders in the current dir, into the destination you have specified in the second quotation marks.

Going into directories in Bash

To go into a directory, you would do.

cd app/app

Execute node app

Go into the directory where your package.json is and run.

This will start the app during the launch of the vm.

cd app/app
npm install
npm start -d

Variables in Bash

Creating and calling variables

Creating and calling a variable with linux will look like this Good to write in captial letters, (good practice)

MY_NAME=Florent
echo $MY_NAME

Prints

Florent

It's not persistent/constant when creating a variable as it will only create it in that terminal/instance.

To make it permanent, you need to add it within the .bashrc file or another hidden file and source it so that the file stays there when you restart the virtual machine

Environment variables

Add export MY_NAME=Florent in the .bashrc file.

> source .bashrc
> printenv MY_NAME

This prints your name and now when you back out of the virtual machine and come back in, you should still be able to print the env.

Reverse Proxy

Reverse proxying is a type of proxy server that sits behind the firewall in a private newtwork and directs client requests to the appropriate backend server. Also provides an additional layer of abstraction and control to ensure smooth flow of network traffic between clients and servers.

A traditional forward proxy server allows multiple clients to route traffic to an external network. For instance, a business may have a proxy that routes and filters employee traffic to the public Internet.

This is what I added in my default file in nginx

  • I deleted the default file
  • Replaced it with a pre-configured file that I made.
  • Replaced the port number to the one node uses.
server {
        listen 80 default_server;
        listen [::]:80 default_server;

        root /var/www/html;

        index index.html index.htm index.nginx-debian.html;

        server_name _;

        location / {
                # First attempt to serve request as file, then
                # as directory, then fall back to displaying a 404.
                try_files $uri $uri/ =404;
                proxy_pass http://localhost:3000;
                proxy_http_version 1.1;
                proxy_set_header Upgrade $http_upgrade;
                proxy_set_header Connection "upgrade";
                proxy_set_header Host $host;
                proxy_cache_bypass $http_upgrade;
        }

}

After you added it, run

sudo nginx -t to make sure that there are no syntax errors

sudo systemctl restart nginx to restart nginx and set up the reverse proxy

You always have to change the port number after the colon to match your needs

location allows you to provide access to other applications on the same server. For example, if location /some/path/, the url would be http://www.example.com/some/path/index.html

proxy_pass passes the url through to a HTTP server