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📂 Chapter 05: File & Directory Operations

Beginner Chapter 05

📑 Table of Contents

Creating Files & Directories

Create Files

touch newfile.txt               # Create empty file (or update timestamp)
touch file1.txt file2.txt       # Create multiple files at once
touch /tmp/test-{1..10}.txt     # Create test-1.txt through test-10.txt

echo "Hello" > hello.txt        # Create file with content (overwrites)
echo "World" >> hello.txt       # Append to file

cat > notes.txt << EOF          # Multi-line content using heredoc
Line 1: This is my notes file
Line 2: Learning Linux is fun
EOF

printf "Name: %s\nAge: %d\n" "Sovon" 25 > info.txt

Create Directories

mkdir mydir                     # Create a single directory
mkdir dir1 dir2 dir3            # Create multiple directories
mkdir -p parent/child/grandchild  # Create nested directories (-p = parents)
mkdir -pv project/{src,docs,tests}  # Create project structure (-v = verbose)
# Create a complete project structure in one command
mkdir -pv myproject/{src/{main,utils},docs,tests,config}

Copying Files & Directories

cp — Copy

cp file.txt backup.txt              # Copy file
cp file.txt /tmp/                   # Copy to another directory
cp file.txt /tmp/newname.txt        # Copy with new name
cp -i file.txt backup.txt           # Prompt before overwrite (-i = interactive)
cp -v file.txt backup.txt           # Show what's being done (-v = verbose)
cp -p file.txt backup.txt           # Preserve timestamps & permissions

# Copy directories (MUST use -r)
cp -r mydir/ mydir-backup/          # Copy directory recursively
cp -rv /etc/nginx/ /tmp/nginx-bak/  # Copy with verbose output
cp -a source/ dest/                 # Archive mode (preserves everything: -r + -p + links)

🚨 Common Mistake: Forgetting -r when copying directories will give an error.

Moving & Renaming

mv — Move and Rename

# Move files
mv file.txt /tmp/                   # Move to /tmp
mv file.txt /tmp/newname.txt        # Move and rename
mv *.log /var/log/                  # Move all .log files

# Rename (same directory = rename)
mv oldname.txt newname.txt          # Rename a file
mv old-dir/ new-dir/               # Rename a directory

# Safety options
mv -i source dest                   # Prompt before overwrite
mv -v source dest                   # Verbose output
mv -n source dest                   # Never overwrite (no-clobber)

# Move multiple files to a directory
mv file1.txt file2.txt file3.txt /backup/

💡 Tip: mv works on both files and directories — no -r flag needed (unlike cp).

Deleting Files & Directories

rm — Remove

rm file.txt                     # Delete a file (permanent!)
rm -i file.txt                  # Prompt before deleting
rm -v file.txt                  # Verbose
rm file1.txt file2.txt          # Delete multiple files
rm *.tmp                        # Delete all .tmp files

# Delete directories
rm -r mydir/                    # Delete directory and contents recursively
rm -ri mydir/                   # Recursive with confirmation for each file
rm -rf mydir/                   # Force delete (no prompts, no errors)

🚨 DANGER ZONE: rm -rf / will destroy your entire system. There is NO recycle bin, NO undo. Always double-check before using rm -rf.

rmdir — Remove Empty Directories

rmdir emptydir                  # Only works if directory is empty
rmdir -p parent/child/grandchild  # Remove nested empty directories

Safer Alternatives

# Use trash-cli instead of rm
sudo apt install trash-cli
trash-put file.txt              # Move to trash
trash-list                      # List trashed files
trash-restore                   # Restore a file
trash-empty                     # Empty the trash

Viewing File Contents

Command Use Case Memory Usage
cat Small files Loads entire file
less Large files Loads page by page
more Large files Older, less features
head First N lines Minimal
tail Last N lines Minimal
nl With line numbers Loads entire file 
# cat — concatenate and display
cat file.txt                    # Display entire file
cat -n file.txt                 # Show with line numbers
cat -A file.txt                 # Show hidden characters (tabs, line endings)
cat file1.txt file2.txt > merged.txt  # Concatenate files

# less — paginated viewing (most useful for large files)
less /var/log/syslog
# Navigation: Space=next page, b=back, /=search, q=quit, g=top, G=bottom

# head — first lines
head file.txt                   # First 10 lines (default)
head -n 5 file.txt              # First 5 lines
head -c 100 file.txt            # First 100 bytes

# tail — last lines
tail file.txt                   # Last 10 lines (default)
tail -n 20 file.txt             # Last 20 lines
tail -f /var/log/syslog         # Follow file in real-time (great for logs!)
tail -F /var/log/syslog         # Follow even if file is rotated

# nl — number lines
nl file.txt                     # Number non-empty lines
nl -ba file.txt                 # Number ALL lines

# Other viewers
tac file.txt                    # cat in reverse (last line first)
rev file.txt                    # Reverse each line
wc file.txt                     # Count lines, words, characters
wc -l file.txt                  # Count lines only

Finding Files

find — The Powerful Finder

# Basic syntax: find [path] [criteria] [action]

# Find by name
find / -name "passwd"                     # Exact name (case-sensitive)
find / -iname "readme.md"                 # Case-insensitive
find /home -name "*.txt"                  # All .txt files
find . -name "*.log" -o -name "*.tmp"     # .log OR .tmp files

# Find by type
find /var -type f                         # Files only
find /var -type d                         # Directories only
find /dev -type l                         # Symbolic links only

# Find by size
find / -size +100M                        # Larger than 100 MB
find / -size -1k                          # Smaller than 1 KB
find . -size 0                            # Empty files
find /var -type f -empty                  # Empty files

# Find by time
find / -mtime -7                          # Modified in last 7 days
find / -atime +30                         # Accessed more than 30 days ago
find / -mmin -60                          # Modified in last 60 minutes
find / -newer reference.txt              # Newer than reference file

# Find by permissions
find / -perm 777                          # Exact permission 777
find / -perm -u=x                         # User has execute permission
find /tmp -writable                       # Writable by current user

# Find by owner
find /home -user sovon                    # Owned by user
find / -group docker                      # Owned by group

# Actions on found files
find . -name "*.tmp" -delete              # Delete found files
find . -name "*.sh" -exec chmod +x {} \;  # Make all .sh files executable
find . -name "*.log" -exec gzip {} \;     # Compress all log files
find . -type f -name "*.txt" -exec grep -l "error" {} \;  # Find files containing "error"

locate — Fast Filename Search

# Uses a pre-built database (faster than find, but not real-time)
sudo apt install mlocate
sudo updatedb                             # Update the database

locate passwd                             # Find all files with "passwd" in the path
locate -i readme                          # Case-insensitive search
locate -c "*.conf"                        # Count matches
locate --regex "\.conf$"                  # Use regex

which, whereis, type

which python3          # Full path to executable
whereis ls             # Binary, source, and man page locations
type cd                # Show if built-in, alias, or binary

Links — Hard & Symbolic

Symbolic Links (Soft Links)

A symlink is a pointer to another file — like a shortcut.

ln -s /path/to/original /path/to/link

# Example
ln -s /var/log/syslog ~/syslog-shortcut
ls -l ~/syslog-shortcut
# lrwxrwxrwx 1 sovon sovon 15 Feb 22 10:00 syslog-shortcut -> /var/log/syslog

Hard Links

A hard link is a direct reference to the same data on disk.

ln original.txt hardlink.txt

# Both point to the same inode (data on disk)
ls -li original.txt hardlink.txt
# 12345 -rw-r--r-- 2 sovon sovon 100 Feb 22 10:00 original.txt
# 12345 -rw-r--r-- 2 sovon sovon 100 Feb 22 10:00 hardlink.txt

Symlink vs Hard Link

Feature Symbolic Link Hard Link
Can link to directories ✅ Yes ❌ No
Can cross filesystems ✅ Yes ❌ No
Breaks if target deleted ✅ Yes (dangling link) ❌ No (data remains)
Has its own inode ✅ Yes ❌ No (shares inode)
Shows as link in ls -l ✅ l prefix ❌ Regular - prefix

Wildcards & Globbing

Wildcards (globbing patterns) let you match multiple files:

Pattern Matches Example
* Any characters (zero or more) *.txt → all .txt files
? Any single character file?.txt → file1.txt, fileA.txt
[abc] Any one of a, b, or c file[123].txt → file1.txt, file2.txt
[a-z] Any character in range file[a-z].txt → filea.txt, fileb.txt
[!abc] NOT a, b, or c file[!0-9].txt → fileA.txt, not file1.txt
{a,b,c} Brace expansion file.{txt,md} → file.txt, file.md 
# Examples
ls *.conf                       # All .conf files
ls image?.png                   # image1.png, imageA.png, etc.
ls log-[0-9][0-9].txt           # log-01.txt through log-99.txt
cp *.{jpg,png,gif} /images/    # Copy all image files
rm temp*                        # Delete all files starting with "temp"

File Metadata

# File type and info
file document.pdf               # PDF document, version 1.4
file script.sh                  # ASCII text, Bash script

# Detailed file status
stat myfile.txt
# Shows: size, blocks, inode, permissions, timestamps, etc.

# Disk usage
du -sh mydir/                   # Total size of directory
du -sh *                        # Size of each item in current directory
du -ah mydir/ | sort -rh | head -10  # Top 10 largest files

# Disk free space
df -h                           # Free space on all mounted filesystems
df -h /home                     # Free space on /home partition

🏋️ Practice Exercises

  1. Create a directory structure: project/{src,docs,tests,build}
  2. Create 5 files: touch project/src/file{1..5}.py
  3. Copy the src directory to src-backup
  4. Rename project/docs to project/documentation
  5. Find all .py files in your home directory: find ~ -name "*.py"
  6. Symlink: Create a link from ~/quick-access to project/
  7. View: Use head, tail, and less on /etc/passwd
  8. Wildcards: List all files in /etc that end with .conf
  9. Size: Find files larger than 10 MB in /var: find /var -size +10M
  10. Clean up: Delete all .tmp files in /tmp

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