What is the Terminal?#

The Linux terminal is a text-based interface where you type commands and get results immediately. It is one of the most powerful parts of Linux because it allows faster control, scripting, and automation than clicking through menus.

Command Structure#

A command usually follows this pattern:

command [options] [arguments]

• Command — Tells Linux what to do
• Options — Change how the command behaves (usually start with - or --)
• Arguments — The files or targets being used

Example#

ls -l /home

• ls = List command
• -l = Option for long format
• /home = Argument (the directory to list)

Result: “List files in long format inside /home”

Basic Navigation#

The most common commands for moving around the filesystem are pwd, ls, and cd.

PWD — Print Working Directory#

Shows the current working directory, which tells you exactly where you are.

$ pwd
/home/user/documents

LS — List Directory Contents#

Lists files and folders in the current directory.

# Basic listing
ls

# Useful options
ls -a        # Show hidden files (starting with .)
ls -l        # Show detailed information (permissions, owner, size, date)
ls -lh       # List with human-readable file sizes
ls -la       # Combine -l and -a
ls -S        # Sort by file size
ls -t        # Sort by modification time
ls *.txt     # Show only .txt files

CD — Change Directory#

Changes the current directory to another folder.

# Navigate to home directory
cd ~
cd /home/user

# Go up one level
cd ..

# Go to root directory
cd /

# Go to previous directory
cd -

# Go to home directory (shortcut)
cd

Core File Commands#

Linux has very simple commands for creating and managing files and directories.

MKDIR — Make Directory#

Creates a new directory.

# Create a single directory
mkdir notes

# Create nested directories
mkdir -p path/to/nested/folder

TOUCH — Create or Update File#

Creates an empty file or updates its timestamp.

# Create a new empty file
touch file.txt

# Create multiple files
touch file1.txt file2.txt file3.txt

# Update the timestamp of an existing file
touch existing_file.txt

CP — Copy#

Copies a file or directory.

# Copy a file
cp source.txt destination.txt

# Copy to a directory
cp file.txt /path/to/destination/

# Copy a directory and its contents
cp -r source_folder/ destination_folder/

# Copy with verbose output
cp -v file.txt destination.txt

MV — Move or Rename#

Moves a file or renames it.

# Move a file to another directory
mv file.txt /path/to/destination/

# Rename a file
mv old_name.txt new_name.txt

# Move and rename
mv source_file.txt /path/to/destination/new_name.txt

# Move multiple files
mv file1.txt file2.txt /destination/

RM — Remove#

Deletes a file. Be careful — deleted files usually do not go to a recycle bin!

# Remove a single file
rm file.txt

# Remove multiple files
rm file1.txt file2.txt file3.txt

# Remove a directory and everything inside it
rm -r folder_name

# Remove with confirmation
rm -i file.txt

# Remove without confirmation (dangerous!)
rm -f file.txt

RMDIR — Remove Directory#

Removes an empty directory.

# Remove empty directory
rmdir empty_folder

# Remove only if empty (safe)
rmdir folder_name

Practical Example#

# Create a folder for assignments
mkdir notes

# Add a file using touch
touch day1.txt

# Copy it for backup
cp day1.txt day1_backup.txt

# Rename the original
mv day1.txt lesson1.txt

# Later, clean up old practice folders
rm -r notes

File Viewing Commands#

A major part of Linux work is reading files from the terminal.

CAT — Concatenate and Display#

Displays the full contents of a file. Best for small files.

# Display a file
cat file.txt

# Display multiple files
cat file1.txt file2.txt

# Display with line numbers
cat -n file.txt

# Display with visible special characters
cat -A file.txt

MORE — View One Screen at a Time#

Shows one screen at a time, useful for longer files.

# View file one screen at a time
more large_file.txt

# Press spacebar to go to next screen
# Press 'q' to quit

LESS — Better Scrolling#

Similar to more but allows easier backward and forward scrolling.

# View with better navigation
less large_file.txt

# Commands while viewing:
# Space  = next page
# b      = previous page
# /word  = search
# q      = quit

HEAD — Show Beginning#

Shows the first lines of a file (default: 10 lines).

# Show first 10 lines
head file.txt

# Show first 20 lines
head -n 20 file.txt
head -20 file.txt

# Show first 5 lines
head -5 file.txt

TAIL — Show End#

Shows the last lines of a file.

# Show last 10 lines
tail file.txt

# Show last 20 lines
tail -n 20 file.txt
tail -20 file.txt

# Follow a file as it grows (useful for logs)
tail -f /var/log/syslog

When to Use Each Command#

For small files       → cat
For long files       → less (or more)
For log files        → tail -f
For first N lines    → head -n N
For last N lines     → tail -n N

Searching Text#

Searching is one of the most useful Linux skills. The grep command is used to find words or patterns inside files.

GREP — Search Text#

Searches for matching lines in files.

# Basic search
grep word file.txt

# Search case-insensitive
grep -i word file.txt

# Search recursively in all files
grep -r word .

# Show line numbers
grep -n word file.txt

# Count matching lines
grep -c word file.txt

# Invert match (show non-matching lines)
grep -v word file.txt

# Show lines before and after
grep -B 2 -A 2 word file.txt

SORT — Sort Lines#

Sorts lines in a file.

# Sort alphabetically
sort file.txt

# Sort numerically
sort -n file.txt

# Sort in reverse
sort -r file.txt

# Sort and remove duplicates
sort -u file.txt

UNIQ — Remove Duplicates#

Removes duplicate adjacent lines.

# Remove duplicate adjacent lines
uniq file.txt

# Show only duplicates
uniq -d file.txt

# Count duplicates
uniq -c file.txt

WC — Word Count#

Counts lines, words, and characters.

# Count lines, words, bytes
wc file.txt

# Count only lines
wc -l file.txt

# Count only words
wc -w file.txt

# Count only characters
wc -c file.txt

CUT — Extract Columns#

Extracts parts of each line.

# Extract first 5 characters
cut -c1-5 file.txt

# Extract specific columns
cut -f1,3 file.txt

TR — Transform Characters#

Transforms characters.

# Convert lowercase to uppercase
tr 'a-z' 'A-Z' < file.txt

# Remove characters
tr -d 'a-z' < file.txt

Practical Examples#

# Search for error in logs
grep error /var/log/syslog

# Find all Python files
grep -r "def " *.py

# Sort a list and remove duplicates
sort file.txt | uniq

# Count lines in a file
wc -l file.txt

# Convert to uppercase
cat file.txt | tr 'a-z' 'A-Z'

Checking System Status#

Some simple commands help you check system status and user details.

WHOAMI — Current User#

Shows the current user.

$ whoami
user

UNAME — System Information#

Shows kernel and system information.

# All system information
uname -a

# Kernel name only
uname -s

# Kernel release
uname -r

# Hardware platform
uname -m

DATE — Current Date and Time#

Displays the current date and time.

# Display current date and time
date

# Format custom output
date "+%Y-%m-%d %H:%M:%S"

HISTORY — Command History#

Shows previously typed commands.

# Show all history
history

# Show last 20 commands
history 20

# Execute a command from history
!50   # Run command #50
!ls   # Run last command starting with 'ls'

CLEAR — Clear Screen#

Cleans the terminal screen.

clear

DF — Disk Usage#

Shows disk usage in a readable format.

# Show disk usage
df

# Show in human-readable format
df -h

# Show inode usage
df -i

FREE — Memory Usage#

Shows memory usage.

# Show memory usage
free

# Show in human-readable format
free -h

# Show in megabytes
free -m

Learning from the System#

Linux is designed so users can learn commands from the system itself.

MAN — Manual Pages#

Opens the manual page for a command.

# Read manual for a command
man ls
man grep
man chmod

# Search within manual
/search_word

# Quit manual
q

HELP FLAG — Quick Help#

Gets a short explanation of available options.

# Quick help
ls --help
grep --help
cd --help

WHATIS — Command Description#

Gives a one-line description.

whatis ls
whatis grep
whatis pwd

WHEREIS — Locate Files#

Shows where the binary and manual files are located.

whereis ls
whereis python

Understanding Paths#

A path tells Linux where a file or folder is located.

Wildcards#

Wildcards are special symbols used to match multiple files.

Practical Examples#

# List all text files
ls *.txt

# Remove files like file1.txt or fileA.txt
rm file?.txt

# Copy all JPG images into a folder
cp *.jpg images/

# Move all PDFs
mv *.pdf documents/

# List files starting with test
ls test*

# List all files and folders (including hidden)
ls -la

Understanding File Permissions#

Even with simple commands, it is useful to know that Linux protects files using permissions. When you run ls -l, you can see whether a file is readable, writable, or executable.

Viewing Permissions#

$ ls -l
-rw-r--r-- 1 user group  1234 May 25 10:30 file.txt
│ └┬┘ └┬┘ └┬┘
│  │   │   └─ Others
│  │   └───── Group
│  └───────── Owner
└────────────── File type

Permission Commands#

Impact of Permissions#

If you do not have permission, the command may fail even if the file exists.

# If you get permission denied
Permission denied

# Change permissions to allow
chmod +x script.sh

# Change owner
chown user:group file.txt

Managing Running Programs#

Some simple Linux commands help you work with running programs and services.

PS — Process Status#

Shows running processes.

# Show all processes
ps aux

# Show specific process
ps aux | grep python

# Show process tree
ps aux --forest

TOP — System Activity#

Shows live system activity and resource usage.

# Show live system activity
top

# Show specific process
top -p 1234

KILL — Stop Process#

Stops a process.

# Kill a process by PID
kill 1234

# Force kill
kill -9 1234

SYSTEMCTL — Control Services#

Controls system services.

# Start a service
sudo systemctl start service_name

# Stop a service
sudo systemctl stop service_name

# Check status
sudo systemctl status service_name

Practical Use#

# Find which program is using too much CPU
top

# Kill a frozen process
kill 1234

# Restart a service
sudo systemctl restart nginx

Basic Network Testing#

A few beginner-friendly commands are useful for checking network connectivity.

PING — Test Connectivity#

Tests whether a system is reachable.

# Ping a host
ping google.com

# Ping with limited attempts
ping -c 4 google.com

# Ping with timeout
ping -w 5 google.com

TRACEROUTE — Show Network Path#

Shows the path packets take to reach a destination.

traceroute google.com

SS or NETSTAT — Open Ports#

Shows open ports and connections.

# Show all connections
ss -a

# Show listening ports
ss -l

# Show TCP connections
ss -t

# Show with process info
ss -tlnp

Hands-On Practice#

Here is a simple practice sequence to understand how commands work together:

# 1. Show current directory
pwd

# 2. List all files including hidden
ls -la

# 3. Create a new directory
mkdir test

# 4. Change to the new directory
cd test

# 5. Create a file
touch sample.txt

# 6. Add content using echo
echo "Hello Linux" > sample.txt

# 7. Display the file content
cat sample.txt

# 8. Go back to parent directory
cd ..

# 9. Remove the test directory
rm -r test

# 10. Verify it's deleted
ls -la

What You Learned#

• Navigation (pwd, cd, ls)
• Directory creation (mkdir)
• File creation (touch)
• Redirecting output (>)
• Viewing files (cat)
• Cleaning up (rm -r)

Case Sensitivity#

Linux is case-sensitive, so these are different files:

• File.txt
• file.txt
• FILE.TXT

Dangerous Commands#

Be careful with rm because deleted files usually do not go to a recycle bin!

# DANGEROUS - Removes everything!
rm -r /

# Safe alternative - use trash-cli
trash-put file.txt

Missing Options#

Some commands need options, not just file names:

# Wrong - won't work for folders
rm folder

# Correct - use -r for directories
rm -r folder

# Wrong - won't show hidden files
ls

# Correct - use -a to show hidden files
ls -a

Forgetting Paths#

# If file is in another directory, use full path
cat /home/user/documents/file.txt

# Not just the filename
cat file.txt   # May not work if not in current directory

Navigation and File Management#

File Viewing#

Text Processing#

System Information#

Help and Documentation#

Processes and Services#

Network Commands#

Key Takeaways#

• Terminal is powerful — Faster than GUI for many tasks
• Commands follow a pattern — command [options] [arguments]
• Practice regularly — Type commands yourself to build muscle memory
• Use help — man and --help are always available
• Be careful with dangerous commands — Especially rm
• Learn gradually — Master basics before advanced topics

Next Steps#

1. Open a terminal
2. Practice each command category
3. Use man when you need details
4. Combine commands to solve real problems
5. Master scripting to automate tasks