Claude Code CLI Skill | Agent Skills

Claude Code CLI

Source: Claude Code CLI Reference, Headless Usage

Installation

# Native (recommended)
curl -fsSL https://claude.ai/install.sh | bash

# NPM (deprecated)
npm install -g @anthropic-ai/claude-code

Verify: claude --version

Authentication

Environment Variables

| Variable | Description | Priority | |----------|-------------|----------| | ANTHROPIC_API_KEY | API key from console.anthropic.com | High (overrides OAuth) | | CLAUDE_CODE_OAUTH_TOKEN | OAuth token for subscription auth | Normal |

Warning: Setting ANTHROPIC_API_KEY bypasses subscription and uses pay-as-you-go API rates.

For Headless/Sandbox Use

Since Claude Code requires browser-based OAuth, use one of:

API Key (recommended for CI/sandboxes):

export ANTHROPIC_API_KEY="sk-ant-..."
claude -p "your prompt"

OAuth Token Transfer (from authenticated machine):

# On local machine: authenticate normally, then copy token
# Location: ~/.config/claude-code/auth.json
# Transfer to sandbox via environment variable
export CLAUDE_CODE_OAUTH_TOKEN="token-from-auth-json"

Check Current Auth

In interactive mode: /status

Non-Interactive Mode (-p / --print)

For automated execution, use -p flag:

claude -p "your prompt here"

This runs the prompt and exits (no REPL).

Essential Flags

Core Flags

| Flag | Description | Example | |------|-------------|---------| | -p, --print | Non-interactive mode, exit after response | claude -p "explain this" | | -c, --continue | Continue most recent conversation | claude -c -p "now fix it" | | -r, --resume <id> | Resume specific session | claude -r "abc123" "continue" | | --model <name> | Set model (sonnet, opus, or full name) | claude --model opus -p "..." |

Permission & Security

| Flag | Description | |------|-------------| | --dangerously-skip-permissions | Skip ALL permission prompts (use with caution) | | --allowedTools <tools> | Auto-approve specific tools without prompting | | --disallowedTools <tools> | Block specific tools entirely | | --permission-mode <mode> | Start in specific mode (e.g., plan) |

Tool Control

# Allow specific tools (comma-separated)
claude -p "fix the bug" --allowedTools "Read,Edit,Bash"

# Allow with prefix matching (e.g., any git command)
claude -p "commit changes" --allowedTools "Bash(git:*)"

# Disable all tools
claude -p "explain this" --tools ""

# Use only specific tools
claude -p "review code" --tools "Read,Grep,Glob"

Output Formats

| Flag | Value | Description | |------|-------|-------------| | --output-format | text | Plain text (default) | | | json | JSON with metadata | | | stream-json | Newline-delimited JSON streaming |

# Get JSON output
claude -p "summarize" --output-format json

# Parse with jq
claude -p "summarize" --output-format json | jq -r '.result'

# Structured output with schema
claude -p "list functions" --output-format json \
  --json-schema '{"type":"object","properties":{"functions":{"type":"array","items":{"type":"string"}}}}'

System Prompt

| Flag | Description | |------|-------------| | --system-prompt <text> | Replace entire system prompt | | --append-system-prompt <text> | Add to default prompt (recommended) | | --system-prompt-file <path> | Load replacement from file | | --append-system-prompt-file <path> | Append from file |

# Append custom instructions (keeps defaults)
claude -p "review this" --append-system-prompt "Focus on security vulnerabilities"

# Replace entire prompt
claude -p "task" --system-prompt "You are a Python expert"

Budget & Limits

| Flag | Description | |------|-------------| | --max-budget-usd <amount> | Maximum spend (print mode only) | | --max-turns <n> | Limit agentic turns (print mode only) |

claude -p "refactor this file" --max-budget-usd 5.00 --max-turns 10

Session Management

# Get session ID from output
session_id=$(claude -p "start review" --output-format json | jq -r '.session_id')

# Resume later
claude -p "continue" --resume "$session_id"

# Continue most recent
claude -p "what was I doing?" --continue

Recommended Sandbox Configuration

For running in Daytona sandboxes:

# Full automated execution with tool access
ANTHROPIC_API_KEY="sk-ant-..." claude -p "Create a hello world Python script" \
  --dangerously-skip-permissions \
  --output-format json \
  --max-turns 20

# Or with specific tool allowlist
ANTHROPIC_API_KEY="sk-ant-..." claude -p "Fix the bug in auth.py" \
  --allowedTools "Read,Edit,Bash,Grep,Glob" \
  --output-format json

# With OAuth token instead
CLAUDE_CODE_OAUTH_TOKEN="token..." claude -p "Explain this codebase" \
  --dangerously-skip-permissions

Exit Codes

| Code | Meaning | |------|---------| | 0 | Success | | 1 | Error (check stderr) |

Piped Input

# Pipe file content
cat src/main.ts | claude -p "explain this code"

# Pipe command output
git diff | claude -p "review these changes"

# Pipe multiple files
cat src/*.ts | claude -p "find security issues"

Common Patterns

Code Review

git diff HEAD~1 | claude -p "Review these changes for bugs and improvements" \
  --append-system-prompt "Focus on security and performance" \
  --output-format json

Bug Fix

claude -p "Fix the failing test in tests/auth.test.ts" \
  --allowedTools "Read,Edit,Bash(npm test:*)" \
  --max-turns 15

Code Generation

claude -p "Create a REST API endpoint for user registration" \
  --dangerously-skip-permissions \
  --max-turns 30

Explanation Only (No Tools)

cat complex-file.ts | claude -p "Explain how this works" --tools ""

Error Messages to Watch For

In sandbox output, watch for:

"Authentication failed" - Invalid token/key
"OAuth token has expired" - Need fresh token
"Invalid API key" - Check ANTHROPIC_API_KEY
"Rate limit exceeded" - Back off and retry
"Context length exceeded" - Reduce input size

Notes

Skills/slash commands (like /commit) only work in interactive mode, not with -p
-p mode exits after completion; use --continue for multi-step tasks
--dangerously-skip-permissions gives full tool access - use in trusted environments only
Output buffering: Claude streams output, buffer at ~100ms for IPC efficiency

Agent Skills: Claude Code CLI

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