/home/alice/Documents/report.txt
/etc/nginx/nginx.conf
/var/log/syslog
/usr/bin/python3

# If you're in /home/alice:
Documents/report.txt              # Same as /home/alice/Documents/report.txt
../bob/file.txt                   # Go up to /home, then into bob/
../../etc/hostname                # Go up twice to /, then into etc/

pwd                    # /home/alice
cd /var/log            # Absolute path to logs
pwd                    # /var/log
cd ~/Projects          # ~ expands to /home/alice
pwd                    # /home/alice/Projects
cd ..                  # Go up one level
pwd                    # /home/alice
cd -                   # Go back to previous directory
pwd                    # /home/alice/Projects

pwd
# Output: /home/alice
 
# After navigating somewhere
cd /var/log
pwd
# Output: /var/log
 
# The environment variable $PWD also contains this info
echo $PWD
# Output: /var/log

# Common pattern: save location, do work elsewhere, return
original_dir=$(pwd)
cd /tmp
# ... do some work ...
cd "$original_dir"  # Return to where you started

# Go to your home directory (all of these are equivalent)
cd
cd ~
cd $HOME
 
# Go to an absolute path
cd /var/log                      # System logs
cd /etc/nginx                    # Nginx configuration
cd /home/alice/Documents         # Specific directory
 
# Go to a relative path (from current location)
cd Documents                     # Move into Documents subdirectory
cd Documents/Projects            # Move into nested directory
cd Projects/my-app/src          # Multiple levels at once
 
# Go up one level (to parent directory)
cd ..
 
# Go up two levels
cd ../..
 
# Go up and into a sibling directory
cd ../other-directory
 
# Go to the previous directory (toggle between two locations)
cd -
 
# Go to another user's home (if you have permission)
cd ~bob

# Start in home directory
cd ~
pwd                              # /home/alice
 
# Navigate to a deeply nested project
cd Documents/Projects/web-app/frontend/src/components
pwd                              # /home/alice/Documents/Projects/web-app/frontend/src/components
 
# Quick jump to parent directory
cd ..
pwd                              # /home/alice/Documents/Projects/web-app/frontend/src
 
# Jump multiple levels up
cd ../../..
pwd                              # /home/alice/Documents/Projects
 
# Toggle between two directories (very useful!)
cd /var/log
pwd                              # /var/log
cd /etc/nginx
pwd                              # /etc/nginx
cd -                             # Back to /var/log
pwd                              # /var/log
cd -                             # Back to /etc/nginx
pwd                              # /etc/nginx
 
# Go to root, then home
cd /
pwd                              # /
cd
pwd                              # /home/alice

# Example: navigating to /etc/nginx/
cd /etc/ng<Tab>          # Completes to: cd /etc/nginx/
cd /etc/nginx/conf<Tab>  # Completes to: cd /etc/nginx/conf.d/
 
# Multiple matches: press Tab twice to see options
cd /etc/n<Tab><Tab>
# Shows: netconfig network/ NetworkManager/ nginx/
 
# You can then type more characters and Tab again
cd /etc/ng<Tab>          # Now completes uniquely to nginx/

# Wrong (interprets as two arguments)
cd My Documents          # Error: bash: cd: My: No such file or directory
 
# Right (quote the path)
cd "My Documents"
cd 'My Documents'
cd My\ Documents         # Escape the space

cd /root                 # Error: Permission denied (unless you're root)
sudo cd /root            # Still doesn't work (cd is a shell builtin)
 
# Solution: Use sudo -i or su to become root first
sudo -i                  # Become root
cd /root                 # Now works

# List files in current directory
ls
 
# List files in a specific directory
ls /etc
 
# List with details (long format)
ls -l
 
# List all files (including hidden files starting with .)
ls -a
 
# Combine options: long format + all files
ls -la
 
# Human-readable file sizes (KB, MB, GB)
ls -lh

ls -l

# Human-readable sizes (KB, MB, GB instead of bytes)
ls -lh
# Output: -rw-r--r--  1 alice  staff  4.0K Jan 15 10:30 document.txt
 
# Sort by modification time (newest first)
ls -lt
 
# Sort by modification time (oldest first)
ls -ltr
 
# Sort by size (largest first)
ls -lS
 
# Sort by size (smallest first)
ls -lSr
 
# Recursive (show contents of subdirectories)
ls -R
 
# Show only directories
ls -d */
 
# One file per line (useful for scripting)
ls -1
 
# Show file type indicators
ls -F
# / = directory, * = executable, @ = symlink, | = pipe
 
# All files, long format, human-readable, sorted by time
ls -alht
 
# List with full timestamps
ls -l --time-style=full-iso
 
# List inode numbers (useful for debugging hard links)
ls -li
 
# List with colors (usually aliased by default)
ls --color=auto

# Find the largest files in a directory
ls -lhS /var/log | head -10
 
# Find recently modified files
ls -lt ~/Documents | head -10
 
# See hidden configuration files in your home directory
ls -la ~ | grep '^\.'
 
# Count files in a directory
ls -1 /etc | wc -l
 
# List only .txt files
ls -la *.txt
 
# List files matching a pattern
ls -la report_202*.pdf
 
# Show directory size summaries with du instead
ls -lh --block-size=M
du -sh */                         # Better for directory sizes
 
# List files modified in the last 24 hours
ls -lt | grep "$(date '+%b %e')"
 
# List files by extension, sorted
ls -la | grep '\.txt$' | sort

# Create multiple files at once
touch file{1,2,3}.txt
# Creates: file1.txt, file2.txt, file3.txt
 
# Numeric ranges
touch file{1..10}.txt
# Creates: file1.txt through file10.txt
 
# Alphabetic ranges
mkdir dir{a..z}
# Creates: dira, dirb, ..., dirz
 
# Combine patterns
touch {report,memo,letter}_{2024..2026}.{txt,pdf}
# Creates: report_2024.txt, report_2024.pdf, report_2025.txt, etc.

# All text files in current directory
ls *.txt
 
# All files starting with "report"
ls report*
 
# Files like data1.csv, data2.csv, ... data9.csv
ls data?.csv
 
# All CSV files
ls *.csv
 
# Files with a vowel as second character
ls ?[aeiou]*
 
# JPEG and PNG images
ls *.{jpg,png,gif}
ls *.jpg *.png *.gif      # Same thing
 
# All files except .log files (requires extglob)
shopt -s extglob
ls !(*.log)
 
# All Python files in all subdirectories (requires globstar)
shopt -s globstar
ls **/*.py
 
# Files modified today
ls -l *.txt | grep "$(date '+%b %e')"
 
# Backup all .conf files
cp /etc/*.conf ~/backup/
 
# Remove all temporary files
rm /tmp/temp_*

# Ubuntu/Debian
sudo apt install tree
 
# macOS
brew install tree
 
# Fedora/RHEL/CentOS
sudo dnf install tree

# Basic usage (show everything in current directory)
tree
 
# Limit depth to 2 levels
tree -L 2
 
# Show only directories (no files)
tree -d
 
# Show hidden files
tree -a
 
# Show file sizes
tree -h
 
# Show file sizes with units
tree -sh
 
# Show only specific file types
tree -P "*.py"           # Only Python files
tree -P "*.{js,ts}"      # JavaScript and TypeScript files
 
# Exclude patterns
tree -I "node_modules|__pycache__|*.pyc"
 
# Show full path for each file
tree -f
 
# Sort by modification time
tree -t
 
# Show permissions
tree -p
 
# Combine options
tree -L 3 -h -a --dirsfirst

tree -L 2 ~/Projects/my-app

file document.txt
# document.txt: UTF-8 Unicode text
 
file photo.jpg
# photo.jpg: JPEG image data, JFIF standard 1.01
 
file script.sh
# script.sh: Bash script, ASCII text executable
 
file /bin/ls
# /bin/ls: ELF 64-bit LSB pie executable, x86-64
 
file archive.tar.gz
# archive.tar.gz: gzip compressed data
 
file mystery_file
# Tells you what it actually is, regardless of name or extension
 
# Check multiple files
file *
 
# Be brief (just show type)
file -b document.txt
# UTF-8 Unicode text
 
# Show MIME type (useful for web servers)
file -i document.txt
# document.txt: text/plain; charset=utf-8

stat document.txt

# Just show modification time (useful in scripts)
stat -c %Y document.txt
# 1705317000
 
# Human-readable format
stat -c "%n: %s bytes, modified %y" document.txt
# document.txt: 4096 bytes, modified 2024-01-15 10:30:00.000000000 +0000

# Get just the filename (remove directory path)
basename /home/alice/Documents/report.txt
# report.txt
 
# Get just the filename without extension
basename /home/alice/Documents/report.txt .txt
# report
 
# Get just the directory path (remove filename)
dirname /home/alice/Documents/report.txt
# /home/alice/Documents

# Process all files in a directory
for file in /var/log/*.log; do
    filename=$(basename "$file")
    dir=$(dirname "$file")
    echo "Processing $filename in $dir"
done