File Operations — Essential Commands

🎯 Learning Objectives

• Create, copy, move, rename, and delete files and directories
• Use wildcards for batch operations
• Understand hard links vs symbolic links
• Use find to locate files

1. Creating Files and Directories

bash
# Create empty file
touch file.txt
touch file1.txt file2.txt file3.txt  # Multiple files
# Create directory
mkdir mydir
mkdir -p path/to/nested/dir  # Create parent directories as needed
mkdir -p {dir1,dir2,dir3}    # Create multiple directories
# Create file with content
echo "Hello, World!" > hello.txt
echo "Line 1" > file.txt      # Overwrite
echo "Line 2" >> file.txt     # Append

2. Listing Files — ls

bash
ls                  # Basic listing
ls -l               # Long format (permissions, owner, size, date)
ls -a               # Show hidden files (starting with .)
ls -la              # Combined
ls -lh              # Human-readable sizes (1K, 2M, 3G)
ls -lt              # Sort by modification time (newest first)
ls -lS              # Sort by file size (largest first)
ls -R               # Recursive (show subdirectories)
ls *.txt            # Wildcard: all .txt files
ls file[0-9].txt    # file1.txt, file2.txt, ..., file9.txt

3. Copying — cp

bash
cp source.txt dest.txt                    # Copy file
cp -i source.txt dest.txt                 # Interactive (prompt before overwrite)
cp -v source.txt dest.txt                 # Verbose (show what's being copied)
cp file.txt /path/to/dir/                 # Copy to directory (same name)
cp -r sourcedir/ destdir/                  # Copy directory recursively
cp -u source.txt dest.txt                 # Copy only if source is newer
# Copy multiple files to directory
cp file1.txt file2.txt file3.txt /target/
cp *.txt /target/                         # Copy all .txt files

4. Moving and Renaming — mv

bash
mv oldname.txt newname.txt    # Rename file
mv file.txt /path/to/dir/     # Move file to directory
mv -i source dest             # Interactive (prompt before overwrite)
mv -v source dest             # Verbose
mv source1 source2 dir/       # Move multiple files to directory
mv dir1/ dir2/                # Rename or move directory

5. Deleting — rm

bash
rm file.txt                   # Delete file
rm -i file.txt                # Interactive (ask before delete)
rm -v file.txt                # Verbose
rm -f file.txt                # Force (no prompt, ignore nonexistent)
rm -r dir/                    # Delete directory recursively
rm -rf dir/                   # Delete directory without prompting ⚠️
# ⚠️ DANGEROUS — be extremely careful:
rm -rf /                      # Delete EVERYTHING (don't run!)
rm -rf ./*                    # Delete all files in current directory

6. Wildcards (Globbing)

bash
# Examples
ls *.txt                    # All text files
ls file[0-9].txt            # file0.txt to file9.txt
cp *.jpg ~/Pictures/        # Copy all JPEGs
rm -rf temp_{1,2,3}/        # Delete temp_1, temp_2, temp_3

7. Finding Files — find

bash
# Basic usage
find . -name "*.txt"             # Find all .txt files starting from current dir
find /home -name "*.pdf"         # Find PDFs in /home
find . -type f -name "*.log"     # Find only files (not directories)
find . -type d -name "backup"    # Find directories named "backup"
# By size
find . -size +1M                 # Files larger than 1 MB
find . -size -10k                # Files smaller than 10 KB
# By time
find . -mtime -7                 # Modified in last 7 days
find . -mmin -60                 # Modified in last 60 minutes
# Execute action on found files
find . -name "*.tmp" -delete     # Delete all .tmp files
find . -name "*.py" -exec wc -l {} \;   # Count lines in Python files
# Combining with xargs
find . -name "*.log" -mtime +30 | xargs rm  # Remove old logs

8. Links — Hard vs Symbolic

bash
# Symbolic link (like a shortcut)
ln -s target.txt link.txt        # Create symbolic link
ls -l                             # Shows link with -> target
# Hard link (another name for same file)
ln target.txt hardlink.txt        # Both point to same inode/data
ls -l                             # Shows link count > 1

9. Practice Questions

Q1: What's the difference between cp and mv?

Answer: cp creates a copy (source remains, new copy created). mv moves/renames (source no longer exists at original location). mv is also used for renaming. Q2: What does mkdir -p a/b/c do?

Answer: Creates nested directories: a, then a/b, then a/b/c. Without -p, it would fail if a or a/b don't exist. Q3: What is the difference between *, ?, and [abc] wildcards?

Answer: * matches any number of characters (including zero). ? matches exactly one character. [abc] matches exactly one character from the set {a, b, c}. Q4: How do you delete a directory and all its contents?

Answer: rm -rf dirname/. -r (recursive) deletes the directory and all contents. -f (force) skips prompts. Be very careful with this command. Q5: What does touch do when the file already exists?

Answer: It updates the file's modification and access timestamps to the current time without changing the file contents. It does NOT delete or modify the file. Q6: What's the difference between a hard link and a symbolic link?

Answer: Symbolic link: points to filename (breaks if target deleted, can cross filesystems). Hard link: points to inode/data (survives original deletion, can't cross filesystems, can't link directories). ls -l shows link type. Q7: How do you find all .log files larger than 100MB?

Answer: find / -name "*.log" -size +100M Q8: What does rm -i do?

Answer: Interactive mode — prompts for confirmation before deleting each file. Useful with wildcards to avoid accidental deletion.

📐 Key Concepts

🔗 Cross-References

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