"Gemini CLI Complete Guide: Google's AI-Powered Command Line Tool for Developers"

# Global install
npm install -g @google/gemini-cli

# Verify installation
gemini --version

# Run directly without installing
npx @google/gemini-cli

git clone https://github.com/google-gemini/gemini-cli.git
cd gemini-cli
npm install
npm run build
npm link

# If you get permission errors
sudo npm install -g @google/gemini-cli
# Or better, use nvm to manage Node.js

# Ensure Node.js 18+
curl -fsSL https://deb.nodesource.com/setup_18.x | sudo -E bash -
sudo apt-get install -y nodejs
npm install -g @google/gemini-cli

# Install in WSL for best experience
wsl
npm install -g @google/gemini-cli

gemini
# First run opens browser for Google OAuth
# After login, you get daily free quota

# Get key from https://aistudio.google.com/apikey
export GEMINI_API_KEY="your-key-here"
gemini

export GOOGLE_CLOUD_PROJECT="your-project-id"
export GOOGLE_CLOUD_REGION="us-central1"
gemini --backend vertex

export GEMINI_API_KEY="your-crazyrouter-key"
export GEMINI_API_BASE="https://api.crazyrouter.com/v1"
gemini

{
  "theme": "dark",
  "model": "gemini-2.5-pro",
  "maxTokens": 8192,
  "temperature": 0.7,
  "systemPrompt": "You are a senior software engineer. Be concise and practical.",
  "safetySettings": {
    "harassment": "BLOCK_NONE",
    "dangerousContent": "BLOCK_NONE"
  }
}

# ~/.gemini/prompts/code-review.txt
You are a strict code reviewer. Focus on:
1. Security vulnerabilities
2. Performance issues
3. Code maintainability
4. Error handling
Rate each area 1-5 and provide specific suggestions.

# Use the custom prompt
gemini --prompt code-review "Review this PR" -f src/

# Start interactive session
gemini

# You're now in a REPL
> Explain the architecture of this project
> What are the main entry points?
> Find potential security issues

# Quick question
gemini "What does this regex do: ^(?=.*[A-Z])(?=.*\d)[A-Za-z\d]{8,}$"

# File analysis
gemini "Explain this code" -f src/auth/middleware.ts

# Multiple files
gemini "How do these files interact?" -f src/api.ts -f src/database.ts -f src/models.ts

# Review staged changes
git diff --staged | gemini "Review these changes for bugs and improvements"

# Review a specific commit
git show abc123 | gemini "Analyze this commit for potential issues"

# Review a PR (all changes from main)
git diff main...HEAD | gemini "Comprehensive code review of this PR"

# Review with custom criteria
git diff --staged | gemini --prompt code-review

# Analyze error logs
cat error.log | gemini "What's causing these errors? Suggest fixes."

# Debug a specific error
gemini "I'm getting this error, what's wrong?" <<'EOF'
TypeError: Cannot read properties of undefined (reading 'map')
    at UserList (/src/components/UserList.tsx:15:23)
    at renderWithHooks (/node_modules/react-dom/cjs/react-dom.development.js:14985:18)
EOF

# Analyze test failures
npm test 2>&1 | gemini "Why are these tests failing?"

# Generate a function
gemini "Write a TypeScript function that debounces API calls with a configurable delay"

# Generate tests
gemini "Generate comprehensive unit tests for this module" -f src/utils/validation.ts

# Generate documentation
gemini "Generate JSDoc comments for all exported functions" -f src/api/handlers.ts

# Find and explain complex functions
grep -rn "async function" src/ | gemini "Which of these functions might have race conditions?"

# Analyze dependencies
cat package.json | gemini "Identify outdated or risky dependencies"

# System diagnostics
docker ps -a --format "table {{.Names}}\t{{.Status}}\t{{.Ports}}" | \
  gemini "Which containers look unhealthy?"

# Database analysis
pg_dump --schema-only mydb | gemini "Suggest index optimizations for this schema"

# Log analysis
journalctl -u myapp --since "1 hour ago" | gemini "Summarize errors and warnings"

# Analyze entire project architecture
find src/ -name "*.ts" | head -50 | xargs gemini "Map the architecture of this project"

# Find dead code
gemini "Identify unused exports and dead code" -f src/

# Security audit
gemini "Perform a security audit. Check for: SQL injection, XSS, CSRF, auth bypass, secrets in code" -f src/

# Migration planning
gemini "I want to migrate from Express to Fastify. Analyze the codebase and create a migration plan" -f src/

# Auto-generate commit messages
git diff --staged | gemini "Write a conventional commit message for these changes"

# Generate changelog
git log --oneline v1.0.0..HEAD | gemini "Generate a user-facing changelog grouped by feature/fix/chore"

# Pre-commit hook
# .git/hooks/pre-commit
#!/bin/bash
DIFF=$(git diff --staged)
REVIEW=$(echo "$DIFF" | gemini "Quick review: any obvious bugs or security issues? Reply YES or NO with brief explanation")
echo "$REVIEW"

# Add type annotations to all Python files
for f in src/**/*.py; do
  echo "Processing $f..."
  gemini "Add type hints to all functions in this file. Output only the modified code." -f "$f" > "${f}.typed"
done

# Generate API docs for all routes
for f in src/routes/*.ts; do
  gemini "Generate OpenAPI 3.0 YAML for the routes in this file" -f "$f" >> api-docs.yaml
done

# Quick code review
alias cr='git diff --staged | gemini "Code review: bugs, security, performance"'

# Explain error
alias explain='gemini "Explain this error and suggest a fix"'

# Generate commit message
alias gcm='git diff --staged | gemini "Write a concise conventional commit message"'

# Quick question about current project
alias ask='gemini -f src/'

# Clear cached credentials
rm -rf ~/.gemini/auth
# Re-authenticate
gemini

# Switch to API key
export GEMINI_API_KEY="your-key"
# Or use Crazyrouter
export GEMINI_API_BASE="https://api.crazyrouter.com/v1"

# Be selective with files
gemini "Review auth logic" -f src/auth/ # Instead of -f src/

# Reduce max tokens
gemini --max-tokens 2048 "Quick answer: what does this function do?" -f utils.ts