Linux Terminal & commands

The Linux Terminal is a way to interact with the machine by typing console commands. To use it, you need an interpreter, like:

• Bourne Again Shell (Bash);
• Z-shell (Zsh);
• KornShell (Ksh);
• C Shell (Csh).

But, don't worry about it. Most Linux distributions comes with one of those by standard, they all are going to work similarly and can do the job.

Directory Structure

Everything starts from the root which is /.

From there:

• /bin essential user binaries;
• /boot boot static files;
• /dev (devices) device files (disks);
• /etc system configuration files (servers like Apache and Nginex);
• /home home directory, which contains users list directory;
• /media mount points for removable media;
• /mnt temporary mount directories;
• /opt optional or third-party software;
• /sbin binary system files;
• /tmp temporary files, non-persistent or cleared on reboot;
• /usr user related programs;
• /var variable files (logs from OS or servers like Apache, Nginx);
• /proc virtual and pseudo files;
• /root home directory of the root user (sudo home).

/ and /root are different things. root is inside /. This folder is used for system adiministrative tasks/files and contains configuration files specific to the root user (or the sudo command).

Commands

Navigation

| Command         | Description                                                 |
|-----------------|-------------------------------------------------------------|
| pwd             | Print working directory                                     |
| ls              | List files and directories (-l, -la, -ls, -lh...)           |
| cd              | Change directory                                            |
| cd ..           | Navigate one folder back in the directory hierarchy         |
| cd -            | Navigate to the folder you was before                       |
| mkdir           | Create folder `mkdir newFolder`                             |
| find            | Search inside current folder (case sensitive: find -i)      |
| locate          | Need to run `updatedb` before `locate index.html`           |
| xdg-open .      | Open current working directory on Files                     |
| xdg-open "path" | Open folder/archive. "xdg-open /home/petry" will open home  |
| xdg-open "file" | "xdg-open index.md" will open index.md form current folder  |

Package Management

| Command         | Description                                                 |
|-----------------|-------------------------------------------------------------|
| apt update      | Updates packages lists. Important before `apt upgrade`      | 
| apt upgrade     | Actually updates the packages (apps).                       | 
| apt search      | Searches for the specific app `apt search <appName>`.       | 
| apt install     | Install app `apt install <appName>`.                        |
| apt remove      | Remove app `apt remove <appName>`.                          |
| apt purge       | Removes app and all dependencies `apt remove <appName>`.    |
| dpkg -l         | Print all apps from packages.                               |
| dpkg -r <app>   | Remove <app>.                                               |

Important files

• cat /etc/apt/sources.list will print where system search for packages.

File management and editing

| Command         | Description                                                 |
|-----------------|-------------------------------------------------------------|
| cp              | Copy. `cp imput.md output.md`                               |
| mv              | Move. `mv file.md /home/petry/Desktop`                      |
| touch index.md  | Creates a new file                                          |
| echo            | Print on screen. `echo "Hello, world!" > hello.md` to save. |
| cat file.md     | Reads and prints file on terminal                           |
| rm / rm -r      | Delete file / delete folder (may need to run as sudo)       |
| code .          | Open directory on Visual Studio Code                        |
| grep            | Search keyword in file (grep "keyword" file.md)             |
| egrep           | Search with multiple keywords (egrep "zsh|bash" file.md)    |
| cut             | Cut selected text inside file                               | 
| sed             | Substitution (sed 's/texto1/texto2' index.md)               | 

Networking and processes

| Command                     | Description                                     |
|-----------------------------|-------------------------------------------------|
| top                         | Print system processes                          |
| ps aux                      | Print all system processes                      |
| ifconfig                    | Print network interfaces                        |
| ip                          | Print network interfaces + IP and MAC addresses |
| systemctl status networking | Print network status                            |  
| systemctl start networking  | Network controls (start, stop, restart)         |
| route                       | Print system routes (route -n)                  | 
| netstat (netstat -l [list]) | Print network open doors and active connections |
| dig +short <url>            | Print IP from from domain (dig +short hello.com)|

Important files

• cat /etc/network/interfaces will print network configuration files.

Utility

| Command         | Description                                                 |
|-----------------|-------------------------------------------------------------|
| setxkbmap br    | Change keyboard language to <country>                       |
| man <app>       | Print manual for <application>                              |
| clear           | Clear terminal window                                       |
| whereis <app>   | Print location if <application> files                       |
| file hello.md   | Print file type (can be used with file name or file path)   |
| xxd hello.md    | Print binaries from file (can be used with path)            |
| curl URL        | Send GET request to URL. Try "curl wttr.in"                 |
| curl -o URL     | Download content (alphabetic "o", not zero)                 |
| !$              | Copy and paste last command entry, to command prompt        |

Remember! Those are not spells. We will get there...

Bonus! Using curl to convert images from the web

Define the output name and file extension after -o. Just like this:

curl -o output.png https://www.thehousedesigners.com/images/uploads/SiteImage-Landing-large-house-plans-1.webp

It works with .webp/.jpeg to .png

Web developers love the .webp/.webm. file format. It is smaller and loads faster. But content creators hate it. .webp/.webm doesn't open on preview apps.

This look shit... Don't worry. I'm working on a cURL post. Maybe after the dig and the traceroute commands.