Linux Command Line Basics - Essential Terminal Commands

Opening the Terminal

On most Linux desktop environments, you can open the terminal with the keyboard shortcut Ctrl + Alt + T. You can also find it in your applications menu under "Terminal", "Console", or "Konsole" depending on your desktop environment.

When the terminal opens, you will see a prompt that typically looks like this:

username@hostname:~$

This tells you your username, the computer name, your current directory (~ means your home folder), and that you are a regular user ($). A # symbol means you are the root (admin) user.

Navigating the File System

The Linux file system starts at the root directory / and branches out into directories. Understanding navigation is the first skill to master.

Command	Description	Example
`pwd`	Print current working directory	`pwd` → /home/user
`ls`	List files and directories	`ls -la` (detailed list with hidden files)
`cd`	Change directory	`cd /var/log`
`cd ..`	Go up one directory level	`cd ..`
`cd ~`	Go to your home directory	`cd ~` or just `cd`
`tree`	Display directory structure as a tree	`tree -L 2` (two levels deep)

# See where you are

$ pwd

/home/user

# List files with details

$ ls -lah

drwxr-xr-x  5 user user 4.0K Apr 11 10:30 Documents

drwxr-xr-x  2 user user 4.0K Apr 10 09:15 Downloads

-rw-r--r--  1 user user  220 Apr  1 12:00 .bashrc

# Navigate to Documents

$ cd Documents

$ pwd

/home/user/Documents

Working with Files and Directories

Command	Description	Example
`touch`	Create an empty file	`touch newfile.txt`
`mkdir`	Create a directory	`mkdir projects`
`mkdir -p`	Create nested directories	`mkdir -p a/b/c`
`cp`	Copy files or directories	`cp file.txt backup.txt`
`mv`	Move or rename files	`mv old.txt new.txt`
`rm`	Remove files	`rm unwanted.txt`
`rm -r`	Remove directories recursively	`rm -r old-project`

Tip: Use rm with caution as there is no trash bin in the terminal. Consider using rm -i for interactive confirmation before each deletion.

Viewing and Editing Files

Command	Description	Example
`cat`	Display entire file contents	`cat config.txt`
`less`	View file with scrolling (press q to quit)	`less /var/log/syslog`
`head`	Show first lines of a file	`head -20 file.txt`
`tail`	Show last lines of a file	`tail -f /var/log/syslog`
`nano`	Simple text editor in the terminal	`nano myfile.txt`
`vim`	Powerful text editor (steep learning curve)	`vim script.sh`

# View a file

$ cat /etc/hostname

my-linux-pc

# Watch a log file in real time

$ tail -f /var/log/syslog

# Edit a file with nano (Ctrl+O to save, Ctrl+X to exit)

$ nano ~/notes.txt

Searching and Finding

Command	Description	Example
`find`	Search for files by name, type, or size	`find / -name "*.conf"`
`grep`	Search text inside files	`grep "error" logfile.txt`
`grep -r`	Search recursively in directories	`grep -r "TODO" ./src`
`which`	Find the location of a command	`which python3`
`locate`	Fast file search using a database	`locate nginx.conf`

Permissions and Ownership

Every file in Linux has permissions that control who can read, write, and execute it. Understanding permissions is essential for security and daily usage.

# View permissions

$ ls -l script.sh

-rwxr-xr-- 1 user group 1024 Apr 11 10:00 script.sh

# Change permissions (make executable)

$ chmod +x script.sh

# Change ownership

$ sudo chown user:group file.txt

# Set specific permissions (owner: rwx, group: rx, others: r)

$ chmod 754 script.sh

The permission string -rwxr-xr-- breaks down as: file type (-), owner permissions (rwx), group permissions (r-x), and others' permissions (r--).

System Information

Command	Description
`uname -a`	Display kernel and system information
`df -h`	Show disk space usage in human-readable format
`free -h`	Display memory usage
`top` or `htop`	Show running processes and resource usage
`whoami`	Display your current username
`uptime`	Show how long the system has been running

Pipes and Redirection

One of the most powerful features of the Linux command line is the ability to chain commands together using pipes (|) and redirect output to files.

# Pipe output from one command to another

$ ls -la | grep ".txt"

# Count the number of files in a directory

$ ls | wc -l

# Redirect output to a file

$ echo "Hello Linux" > greeting.txt

# Append to a file

$ echo "Another line" >> greeting.txt

# Sort and remove duplicates

$ cat names.txt | sort | uniq

Essential Keyboard Shortcuts

Shortcut	Action
`Tab`	Auto-complete commands and file names
`Ctrl + C`	Cancel the current command
`Ctrl + L`	Clear the screen
`Ctrl + R`	Search command history
`Ctrl + A`	Move cursor to the beginning of the line
`Ctrl + E`	Move cursor to the end of the line
`Up Arrow`	Recall the previous command

Tip: Pressing Tab twice shows all possible completions. This is the single most useful habit you can develop when using the terminal.

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