# Check if command exists
which node
which python
command -v node
type node

# Check PATH
echo $PATH
echo $PATH | tr ':' '\n'  # One per line

# Find where a binary lives
which -a python       # All matches in PATH
whereis python       # Binary, source, and man pages

# Common fixes
export PATH="/usr/local/bin:$PATH"           # Prepend
export PATH="$HOME/.local/bin:$PATH"         # User binaries
export PATH="$HOME/.cargo/bin:$PATH"         # Rust
export PATH="$HOME/go/bin:$PATH"             # Go
export PATH="$HOME/.nvm/versions/node/v20.0.0/bin:$PATH"  # nvm

# Make permanent - add to shell config:
# ~/.bashrc (bash), ~/.zshrc (zsh), ~/.profile (login shell)

# Which shell am I using?
echo $SHELL
echo $0

# Config file load order:
# bash login:    /etc/profile → ~/.bash_profile → ~/.bashrc
# bash non-login: ~/.bashrc
# zsh login:     ~/.zprofile → ~/.zshrc
# zsh non-login: ~/.zshrc

# Reload config
source ~/.zshrc
source ~/.bashrc

# Check if interactive/login
[[ $- == *i* ]] && echo "Interactive" || echo "Non-interactive"
shopt -q login_shell && echo "Login" || echo "Non-login"  # bash
[[ -o login ]] && echo "Login" || echo "Non-login"        # zsh

# View all
env
printenv

# View specific
echo $NODE_ENV
printenv NODE_ENV

# Set for current session
export API_KEY="abc123"
export NODE_ENV=production

# Set for single command
NODE_ENV=test npm test
DATABASE_URL=postgres://localhost/test python manage.py migrate

# Unset
unset API_KEY

# Check if set
[ -z "$API_KEY" ] && echo "NOT SET" || echo "SET: $API_KEY"

# .env file loading
# Node.js: dotenv, or node --env-file=.env app.js (Node 20.6+)
# Python: python-dotenv
# Shell: source .env or export $(cat .env | xargs)

# Check file permissions
ls -la /path/to/file

# Permission format: drwxrwxrwx
# d = directory, r = read, w = write, x = execute
# [owner][group][others]

# Make executable
chmod +x script.sh
chmod 755 script.sh    # rwxr-xr-x

# Fix npm global permissions
mkdir ~/.npm-global
npm config set prefix '~/.npm-global'
export PATH="$HOME/.npm-global/bin:$PATH"

# Fix SSH key permissions
chmod 700 ~/.ssh
chmod 600 ~/.ssh/id_rsa
chmod 644 ~/.ssh/id_rsa.pub
chmod 644 ~/.ssh/config

# Check who owns a file
ls -la /usr/local/bin/node

# Fix ownership
sudo chown -R $(whoami) /usr/local/lib/node_modules

# What's using a port?
lsof -i :3000              # macOS/Linux
ss -tlnp | grep 3000       # Linux
netstat -tlnp | grep 3000  # Linux

# Kill process on port
lsof -ti :3000 | xargs kill -9   # macOS/Linux
fuser -k 3000/tcp                 # Linux

# Check if port is available
nc -z localhost 3000 && echo "IN USE" || echo "FREE"

# Multiple Node versions?
which -a node
node --version

# nvm issues
nvm ls                     # List installed versions
nvm use 20                 # Switch version
nvm alias default 20       # Set default
nvm current                # Current version

# npm cache issues
npm cache clean --force
rm -rf node_modules package-lock.json && npm install

# Global packages location
npm root -g
npm list -g --depth=0

# npx not finding package
npx --yes package-name     # Force install
npm exec -- package-name   # Alternative

# Multiple Python versions?
which -a python
which -a python3
python --version
python3 --version

# Virtual environment active?
echo $VIRTUAL_ENV

# Wrong pip?
which pip
pip --version      # Shows which Python it's linked to
python -m pip --version  # Use specific Python's pip

# Module not found?
python -c "import sys; print('\n'.join(sys.path))"
python -c "import package; print(package.__file__)"

# pyenv issues
pyenv versions
pyenv which python
pyenv shell 3.12.1

# DNS resolution
nslookup example.com
dig example.com
host example.com

# Test connectivity
ping -c 3 example.com
curl -v https://example.com

# Check proxy settings
echo $HTTP_PROXY
echo $HTTPS_PROXY
echo $NO_PROXY

# SSL certificate issues
openssl s_client -connect example.com:443

# Test specific port
nc -zv example.com 443
curl -v telnet://example.com:443

# Docker daemon running?
docker info

# Permission denied?
sudo usermod -aG docker $USER
# Then log out and back in

# DNS issues in container
docker run --dns 8.8.8.8 myimage

# Can't connect to container?
docker inspect <container> | grep IPAddress
docker port <container>

# Check disk usage
df -h

# Find large files/dirs
du -sh *
du -sh * | sort -rh | head -20

# Node.js specific
du -sh node_modules/
npx npkill    # Interactive node_modules cleaner

# Docker specific
docker system df
docker system prune -a --volumes

#!/bin/bash
echo "=== System ==="
uname -a
echo ""
echo "=== Shell ==="
echo "$SHELL ($0)"
echo ""
echo "=== PATH ==="
echo $PATH | tr ':' '\n'
echo ""
echo "=== Key Tools ==="
for cmd in node npm python python3 pip git docker; do
  printf "%-10s" "$cmd:"
  command -v $cmd 2>/dev/null && $cmd --version 2>/dev/null | head -1 || echo "NOT FOUND"
done
echo ""
echo "=== Env Vars ==="
for var in NODE_ENV VIRTUAL_ENV HOME USER SHELL TERM; do
  printf "%-15s %s\n" "$var:" "${!var:-NOT SET}"
done