1. Basic Navigation

1.1 cd: Change Directory

# Change to an absolute path
cd /study/files

# Change to a relative path
cd test/

# Special directory shortcuts
cd .      # Current directory
cd ..     # Parent directory
cd /      # Root directory
cd ~      # Home directory

1.2 ls: List Directory Contents

# Basic listing
ls

# Detailed listing
ls -l

# Alias for detailed listing
ll

1.3 pwd: Print Working Directory

# Show current directory path
pwd

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2. System Information

2.1 hostname: Display Host Name

hostname

2.2 who: Show Logged-in Users

who

2.3 whoami: Display Current Usenrame

whoami

2.4 ifconfig: Show Network Interface Configuration

ifconfig

2.5 ping: Test Network Connectivity

ping example.com

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3. File and Dircetory Operations

3.1 mkdir: Create Directories

# Create a single directory
mkdir /usr/local/Test

# Create nested directories
mkdir -p parent/child/grandchild

3.2 touch: Create Empty Files

# Create a file with extension
touch document.txt

3.3 vi: Text Editor

# Open file for editing
vi document.txt

# Editing commands:
# i - Enter insert mode
# ESC - Exit insert mode
# :wq - Save and quit
# :q - Quit (if no changes)
# :q! - Force quit without saving

3.4 cp: Copy Files and Directories

# Copy a file
cp source.txt destination/

# Copy a directory recursively
cp -r source_dir/ destination/

3.5 mv: Move or Rename

# Move a file
mv file.txt new_location/

# Rename a file
mv old_name.txt new_name.txt

3.6 rm: Remove Files and Directories

# Remove a file
rm unwanted_file.txt

# Remove a directory recursively and forcefully
rm -rf unwanted_directory/

# Common options:
# -r: Recursive removal
# -f: Force removal
# -v: Verbose output
# -i: Interactive prompt

3.7 chmod: Change File Permissions

# Change permissions using numeric notation
chmod 755 script.sh

# Change permissions recursively
chmod -R 644 directory/

# Permission values:
# r (read) = 4
# w (write) = 2
# x (execute) = 1
# Example: r-x = 5 (4+1)

3.8 tar: Archive and Compress

# Create a tar archive
tar -cvf archive.tar source_dir/

# Extract a tar archive
tar -xvf archive.tar

# Create a compressed tar archive
tar -zcvf archive.tar.gz source_dir/

# Extract a compressed tar archive
tar -zxvf archive.tar.gz

# Common options:
# c: Create archive
# x: Extract archive
# z: Use gzip compression
# v: Verbose output
# f: Specify filename

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4. File Viewing and Searching

4.1 cat: Display File Contents

cat document.txt

4.2 head: View Beginning of File

# Show first 5 lines
head -5 document.txt

4.3 sed: Extract Specific Lines

# Show lines 5 through 10
sed -n '5,10p' document.txt

4.4 tail: View End of File

# Show last 5 lines
tail -5 document.txt

# Follow file changes in real-time
tail -f logfile.log

4.5 more: View File Page by Page

# View file with pagination
more document.txt

# Start from line 20
more +20 document.txt

4.6 less: Advanced File Viewer

# View file with navigation
less document.txt

4.7 grep: Search Text Patterns

# Basic search
grep "search_term" file.txt

# Case-insensitive search
grep -i "term" file.txt

# Show line numbers
grep -n "term" file.txt

# Search in multiple files
grep "term" *.txt

# Search with color highlighting
grep --color=auto "term" file.txt

4.8 find: Search for Files

# Find file by name
find /usr/local -name "TargetFile"

# Find files with pattern
find /usr/local -name "test*"

4.9 |: Pipe Operator

# Chain commands: find version in last 200 lines
tail -200 log.txt | grep "version"

4.10 Redirection Operators

# Overwrite file
command > output.txt

# Append to file
command >> output.txt

# Force overwrite
command >! output.txt

# Input from file
command < input.txt

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5. User and Group Management

5.1 User Management

# Create a new user
useradd newuser

# Set user password
passwd newuser

# Delete a user
userdel olduser

# Delete user with home directory
userdel -r olduser

# View all users
cat /etc/passwd

5.2 Group Management

# Create a new group
groupadd developers

# Delete a group
groupdel developers

# Add user to group
gpasswd -a username developers

# Remove user from group
gpasswd -d username developers

# Check user's groups
groups username

# View all groups
cat /etc/group