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Linux CLI Essentials

Essential commands for working with the Linux command line.

📅 Date: 04.04.2025

🔹 1. Terminal

A text-based interface to interact with the shell.

🔹 2. Shell

A program that interprets and runs user commands in the terminal.

echo $SHELL
bash

🔹 3. Installing CLI Tools

How to install key tools for Linux terminal work.

sudo apt install vim neovim emacs tree jq graphviz htop sed gzip python3

🔹 4. System Maintenance Commands

Useful daily commands for keeping your Linux system up-to-date and clean.

sudo apt update && sudo apt upgrade
  • sudo apt update — Updates the list of available packages.
    Обновляет список доступных пакетов.
  • sudo apt upgrade — Installs the latest versions of installed packages.
    Устанавливает последние версии установленных программ.
sudo apt remove package-name
  • Removes the specified package from the system.
    Удаляет указанный пакет из системы.
sudo apt autoremove
  • Removes unused dependencies and old package remnants.
    Удаляет неиспользуемые зависимости и остатки от старых пакетов.

📌 It is recommended to run these commands regularly (e.g., daily or weekly) to keep your system clean and secure.

🔹 5. Files and Directories (Viewing and Navigation)

Everything in Linux is a file or directory.

pwd                  # Print current working directory
ls                   # List directory contents (short format)
ls -l                # Long format: permissions, owner, group, size, date, filename
ls -lrt              # Long format + sorted by time (most recent last)
tree -L 2            # Show directory structure as a tree, limited to 2 levels

🔸 ls options explained:

  • -l — long format with detailed file info (permissions, size, date).
  • -r — reverse order (e.g. oldest files first).
  • -t — sort by modification time, newest first.
  • Other useful options:
    • -a — show all files, including hidden (. prefix)
    • -h — human-readable sizes (ls -lh)

🔹 6. Permissions

Rules that define who can read, write, or execute a file.

ls -l
chmod 755 folder
  • r — read permission
  • w — write permission
  • x — execute permission
  • d — directory (if the first character in ls -l — d)

Example: drwxr-xr-x

  • d — directory
  • rwx — owner: read, write, execute
  • r-x — group: read, execute
  • r-x — others: read, execute

🔹 7. Root User & sudo

The most powerful user with full access to the system.

sudo apt update

🔹 8. User and Group Management

Managing users and assigning them to groups for permissions.

groups                  # Show groups for current user
groups username         # Show groups for another user
sudo usermod -aG sudo username     # Add user to sudo group
sudo gpasswd -d username sudo      # Remove user from sudo group
getent group sudo                  # List all members of sudo group

🔹 9. Useful Shortcuts

Shortcuts to navigate and control the terminal efficiently.

history
history | less
Ctrl+D     # exit shell or Python

🔹 10. Searching Command History with grep

Search for specific commands you've used in your history.

history | grep vim
history | grep sudo
history | grep install

🔹 11. Vim / Neovim / Emacs

Install:

sudo apt install emacs

Install:

sudo apt install neovim

Install:

sudo apt install vim

Terminal-based text editors used to write and edit code or configuration files.

vim file.txt
nvim file.txt
emacs file.txt
i       # insert mode
Esc     # back to command mode
:wq     # save and quit
:q!     # quit without saving

🔹 12. sed

Install:

sudo apt install sed

A stream editor used to find and replace text in files.

sed 's/old/new/' file.txt
sed -i 's/old/new/g' file.txt

🔹 13. jq

Install:

sudo apt install jq

A command-line tool for processing and formatting JSON data.

jq '.key' file.json
jq 'keys' file.json
jq '.users[].name' file.json

🔹 14. tree

Install:

sudo apt install tree

Displays the directory structure in a tree format.

tree -L 2
  • -L — limit display depth to N levels (e.g., 2)
  • -a — show all files (including hidden)
  • -d — only show directories

🔹 15. gzip / gunzip / tar

Tools for compressing and decompressing files.

gzip file.txt
gunzip file.txt.gz
tar -czvf archive.tar.gz folder/
tar -xzvf archive.tar.gz

🔹 16. Graphviz / digraph

Install:

sudo apt install graphviz

A tool for visualizing graphs described in DOT language.

digraph authn {
  A -> B
  B -> C
}
dot -Tpng file.dot -o output.png

🔹 17. Python 3

A popular and easy-to-learn programming language.

python3
print("Hello")
Ctrl+D   # exit

🔹 18. Networking with nmcli

Install:

nmcli is included in the network-manager package (default on Debian)

A command-line tool to manage network connections.

nmcli connection show