Week 2 - Day 2: File Operations

📚 Learning Objectives

By the end of this session, you will be able to:

Create, copy, move, and delete files and directories
View and edit file contents
Understand file permissions (rwx)
Change permissions with chmod
Understand file ownership (chown)

📖 Core Concepts (2 Hours)

Creating Files & Directories

                    
# Create empty file
touch myfile.txt
touch file1.txt file2.txt file3.txt

# Create directory
mkdir mydir
mkdir -p parent/child/grandchild  # Create nested dirs

# Create file with content
echo "Hello World" > hello.txt

# Append to file
echo "New line" >> hello.txt
                    
                

Copying, Moving, Deleting

                    
# Copy files
cp source.txt destination.txt
cp file.txt /path/to/destination/
cp -r folder/ newfolder/          # Copy directory recursively

# Move/Rename
mv oldname.txt newname.txt        # Rename
mv file.txt /path/to/destination/ # Move

# Delete (CAREFUL!)
rm file.txt                       # Delete file
rm -r folder/                     # Delete directory
rm -rf folder/                    # Force delete (dangerous!)
rmdir emptydir/                   # Remove empty directory only
                    
                

Viewing File Contents

                    
# View entire file
cat file.txt

# View with line numbers
cat -n file.txt

# View first/last lines
head file.txt           # First 10 lines
head -n 20 file.txt     # First 20 lines
tail file.txt           # Last 10 lines
tail -n 20 file.txt     # Last 20 lines
tail -f /var/log/syslog # Follow file (live updates!)

# Page through file
less file.txt           # Navigate with arrows, q to quit
more file.txt           # Older pager

# Word count
wc file.txt             # lines, words, chars
wc -l file.txt          # Lines only
                    
                

Text Editors

                    
# Nano - Beginner friendly
nano file.txt
# Ctrl+O to save, Ctrl+X to exit

# Vim - Powerful but learning curve
vim file.txt
# i = insert mode
# Esc = normal mode
# :w = save
# :q = quit
# :wq = save and quit
# :q! = quit without saving

# VS Code (if GUI available)
code file.txt
                    
                

File Permissions

                    
# View permissions
ls -l file.txt
# -rw-r--r-- 1 user group 1234 Jan 15 10:00 file.txt

# Permission breakdown:
# -rw-r--r--
# │└┬┘└┬┘└┬┘
# │ │  │  └── Others: read only
# │ │  └───── Group: read only  
# │ └──────── Owner: read, write
# └────────── Type: - file, d directory, l link

# r = read (4)
# w = write (2)
# x = execute (1)

# Change permissions
chmod 755 script.sh     # rwxr-xr-x
chmod 644 file.txt      # rw-r--r--
chmod u+x script.sh     # Add execute for user
chmod g+w file.txt      # Add write for group
chmod o-r file.txt      # Remove read for others
chmod a+r file.txt      # Add read for all

# Common permission patterns
# 755 - Executable scripts
# 644 - Regular files
# 700 - Private files/directories
# 600 - Secure files (SSH keys)
                    
                

File Ownership

                    
# View ownership
ls -l file.txt
# -rw-r--r-- 1 owner group ...

# Change owner
sudo chown newowner file.txt
sudo chown newowner:newgroup file.txt
sudo chown -R owner:group directory/  # Recursive
                    
                

🔬 Hands-on Lab (2.5 Hours)

Lab 1: File Operations Practice

Create a project directory structure
Create, copy, move files between directories
Practice safe deletion

                    
# Lab 1: Create project structure
cd ~
mkdir -p devops-project/{src,config,logs,scripts}

# Create files
touch devops-project/src/app.py
touch devops-project/config/settings.ini
touch devops-project/scripts/deploy.sh
echo "# My DevOps Project" > devops-project/README.md

# View structure
ls -R devops-project/

# Copy/Move practice
cp devops-project/README.md devops-project/README.backup
mv devops-project/scripts/deploy.sh devops-project/scripts/deploy_v1.sh
                    
                

Lab 2: Log File Analysis

Create sample log file
Use head, tail, cat to view
Practice tail -f for live monitoring

                    
# Lab 2: Working with logs
cd ~/devops-project/logs

# Create sample log
cat > app.log << 'EOF'
2024-01-15 10:00:01 INFO Application started
2024-01-15 10:00:02 INFO Loading configuration
2024-01-15 10:00:03 INFO Database connected
2024-01-15 10:01:00 WARNING High memory usage: 80%
2024-01-15 10:02:00 ERROR Connection timeout
2024-01-15 10:02:01 INFO Retrying connection
2024-01-15 10:02:05 INFO Connection restored
2024-01-15 10:03:00 INFO Processing request #12345
2024-01-15 10:04:00 INFO Request completed
2024-01-15 10:05:00 INFO Shutting down
EOF

# View file
cat app.log
head -3 app.log
tail -3 app.log
wc -l app.log
                    
                

Lab 3: Permissions Management

Create a script file
Try to execute (will fail)
Add execute permission
Run the script

                    
# Lab 3: Script permissions
cd ~/devops-project/scripts

# Create script
cat > hello.sh << 'EOF'
#!/bin/bash
echo "Hello from the script!"
echo "Current user: $(whoami)"
echo "Current directory: $(pwd)"
EOF

# Check permissions
ls -l hello.sh
# -rw-r--r-- (no execute permission)

# Try to run (will fail)
./hello.sh
# Permission denied

# Add execute permission
chmod +x hello.sh
# OR
chmod 755 hello.sh

# Check again
ls -l hello.sh
# -rwxr-xr-x

# Now run it
./hello.sh
                    
                

📝 Practice Exercises

Create a directory structure for a web project with css, js, images folders
What permission number gives read+write to owner, read to everyone else?
Create a file and change its permissions to 600. Who can access it?
Practice using nano to edit a configuration file

⚠️ Important Safety Tips

Never run: rm -rf / or rm -rf *
Always double-check: Before any rm command
Use -i flag: rm -i file asks for confirmation
Backup important files: Before making changes

✅ Day 2 Checklist

Can create files and directories
Can copy, move, rename files
Can safely delete files and directories
Can view file contents (cat, head, tail, less)
Understand file permissions (rwx)
Can change permissions with chmod
Understand file ownership