Linux Commands Every Developer Should Know

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File Operations

# Find files by name
find . -name "*.js" -type f

# Find files modified in last 7 days
find . -mtime -7 -type f

# Find large files (>100MB)
find . -size +100M -ls

# Search file contents
grep -r "TODO" .
grep -r "functionName" src/ --include="*.js"

# Replace text in files
sed -i 's/oldText/newText/g' *.js

# Copy with progress
cp -r source/ dest/

# Move/Rename
mv old_name.js new_name.js

# Delete recursively (careful!)
rm -rf node_modules/

Disk & Memory

# Disk usage summary
df -h

# Directory sizes (sorted)
du -sh * | sort -hr

# Top 10 largest files
du -ah . | sort -hr | head -10

# Free memory
free -h

# What's using disk space?
ncdu /          # Interactive disk usage explorer (install first)

# Clean up
sudo apt autoremove    # Remove unused packages
docker system prune -a # Clean Docker unused data
npm cache clean --force # Clear npm cache

Process Management

# Running processes
ps aux | grep node

# Real-time process monitor
htop            # Better top (install: sudo apt install htop)

# Kill process
kill PID
kill -9 PID     # Force kill (use as last resort)

# Kill by name
pkill -f "node server"

# Port in use?
lsof -i :3000
ss -tlnp | grep :3000

# Background process
node server.js &
# Or use nohup for persistent:
nohup node server.js &
disown           # Detach from terminal

Network

# Test connectivity
ping google.com

# DNS lookup
nslookup example.com
dig example.com     # More detailed

# HTTP request (no curl? use this)
wget -qO- https://example.com

# With headers
curl -I https://example.com        # Headers only
curl -v https://example.com       # Verbose

# POST request
curl -X POST https://api.example.com/data \
  -H "Content-Type: application/json" \
  -d '{"key": "value"}'

# Download file
curl -o filename.zip https://example.com/file.zip

# Port scanning (basic)
nmap localhost         # Install: sudo apt install nmap

Text Processing

# View file contents
cat file.txt
less file.txt         # Paginated (q to quit)
head -n 20 file.txt   # First 20 lines
tail -f logfile.txt   # Follow live updates

# Count lines/words/chars
wc -l file.txt        # Lines only
wc -w file.txt        # Words

# Sort
sort file.txt                    # Alphabetical
sort -nr numbers.txt             # Numerical reverse
sort -k2 -t',' file.csv          # By column 2

# Unique values
sort file.txt | uniq              # Deduplicate
sort file.txt | uniq -c           # Count occurrences
sort file.txt | uniq -c | sort -rn | head # Top occurrences

# Column extraction
awk -F',' '{print $1, $3}' data.csv  # Columns 1 and 3
cut -d',' -f1-3 data.csv             # Columns 1-3

Permissions

# Current permissions
ls -la

# Change permissions
chmod 755 script.sh      # rwxr-xr-x
chmod +x script.sh       # Make executable
chmod -R 644 public/     # Recursive (files readable)

# Change owner
chown user:group file
chown -R www-data:www-data public/

# Check current user
whoami
id                        # Groups too

# Switch user
su - username
sudo -u postgres psql     # Run as another user

SSH & Remote

# Connect
ssh user@hostname

# With custom port
ssh -p 2222 user@hostname

# Copy files to remote
scp file.txt user@host:/path/to/dest/
scp -r folder/ user@host:/path/to/dest/

# Copy from remote
scp user@host:/path/file.txt ./

# Key-based auth (no password!)
ssh-keygen -t ed25519    # Generate key
ssh-copy-id user@host    # Copy key to server

# Config file (~/.ssh/config)
Host myserver
    HostName 192.168.1.100
    User ubuntu
    IdentityFile ~/.ssh/id_ed25519
# Now just: ssh myserver

Git Quick Reference

git status                # What changed?
git diff                  # What exactly changed?
git log --oneline -10     # Recent commits
git add -A && git commit -m "msg"  # Stage all + commit
git push origin main      # Push to remote
git pull origin main      # Pull latest
git stash                 # Save work temporarily
git stash pop             # Restore stashed work

System Info

# OS info
uname -a
cat /etc/os-release

# CPU info
nproc                     # Number of cores
lscpu                     # Detailed CPU info

# Uptime
uptime

# Environment variables
env | grep NODE           # Filter by keyword
echo $PATH                # Just PATH
export PATH="$PATH:/new/path"  # Add to PATH

One-Liners That Save Time

# Kill all Node processes
pkill -f node

# Find and replace in all JS files recursively
find . -name "*.js" -exec sed -i 's/old/new/g' {} +

# Watch a command run repeatedly (every 2s)
watch -n 2 'curl -s http://localhost:3000/health'

# Create directory structure
mkdir -p project/{src,test,dist,docs}

# Batch rename files
for f in *.txt; do mv "$f "${f%.txt}.md"; done

# Download entire website
wget --mirror --convert-links --page-requisites https://example.com

# Random password
openssl rand -base64 16

# Base64 encode/decode
echo "text" | base64
echo "dGV4dA==" | base64 -d

# JSON pretty print
echo '{"a":1}' | python3 -m json.tool
curl -s api/data | python3 -m json.tool

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