File Operations Skill

Master file system operations with production-ready patterns

Learning Objectives

After completing this skill, you will be able to:

• Manage file permissions (chmod, chown)
• Search files efficiently with find and fd
• Create and extract archives (tar, zip)
• Synchronize files with rsync
• Work with symbolic and hard links

Prerequisites

• Bash basics
• Understanding of file systems
• Command line navigation

Core Concepts

1. Permission Management

# Numeric notation
chmod 755 script.sh       # rwxr-xr-x
chmod 644 file.txt        # rw-r--r--
chmod 600 secret.key      # rw-------

# Symbolic notation
chmod u+x script.sh       # Add execute for owner
chmod g-w file.txt        # Remove write for group
chmod a+r public.txt      # Add read for all

# Ownership
chown user:group file
chown -R user:group dir/

# Common patterns
chmod 600 ~/.ssh/id_rsa   # SSH private key
chmod 755 /var/www/html/  # Web directory

2. Find Command

# By name
find . -name "*.txt"
find . -iname "*.TXT"     # Case insensitive

# By type
find . -type f            # Files
find . -type d            # Directories
find . -type l            # Symlinks

# By size/time
find . -size +100M        # Larger than 100MB
find . -mtime -7          # Modified in 7 days

# Actions
find . -name "*.tmp" -delete
find . -type f -exec chmod 644 {} +

3. Archive Operations

# Create archives
tar -cvf archive.tar dir/
tar -czvf archive.tar.gz dir/   # gzip
tar -cjvf archive.tar.bz2 dir/  # bzip2

# Extract archives
tar -xvf archive.tar
tar -xzvf archive.tar.gz -C /dest/

# ZIP
zip -r archive.zip dir/
unzip archive.zip

4. Rsync

# Local sync
rsync -avz source/ dest/

# Remote sync
rsync -avz local/ user@host:/remote/

# With delete (mirror)
rsync -avz --delete source/ dest/

# Dry run
rsync -avzn source/ dest/

Common Patterns

Safe Delete Pattern

# With confirmation
rm -i file.txt

# With variable check
rm -rf "${DIR:?}/"   # Fails if DIR empty

Backup Pattern

# Timestamped backup
backup() {
    local src="$1"
    local timestamp=$(date +%Y%m%d_%H%M%S)
    cp -a "$src" "${src}.${timestamp}.bak"
}

Find and Process

# Fix permissions
find /var/www -type d -exec chmod 755 {} +
find /var/www -type f -exec chmod 644 {} +

# Delete old files
find /tmp -type f -mtime +7 -delete

Anti-Patterns

Don't	Do	Why
rm -rf $VAR/	rm -rf "${VAR:?}/"	Empty VAR = delete /
find | xargs rm	find -delete	Handles spaces
cp -r for sync	rsync -a	rsync is smarter

Practice Exercises

1. Permission Fixer: Script to fix web dir permissions
2. Old File Cleaner: Remove files older than N days
3. Backup Script: Timestamped backup with rotation
4. Sync Tool: Two-way directory sync

Troubleshooting

Common Errors

Error	Cause	Fix
Permission denied	Wrong permissions	Check with ls -la
No such file	Path typo	Verify path exists
Directory not empty	rm without -r	Add -r flag
Cross-device link	Hard link across fs	Use symlink

Debug Techniques

# Check permissions
stat file.txt
ls -la file.txt

# Trace find
find . -name "*.txt" -print

# Dry-run rsync
rsync -avzn source/ dest/

Safety Guidelines

1. Always dry-run rsync with --delete first
2. Quote paths with spaces: "$path"
3. Verify paths before rm -rf
4. Use trash instead of rm when possible
5. Backup before bulk operations

Resources

• GNU Coreutils
• find Manual
• rsync Manual
• fd - modern find