command-execution-principles

name	command-execution-principles
description	Apply safe command execution patterns when spawning external processes, shell commands, or system calls from application code. Covers input sanitization, timeout handling, output capture, and error propagation.
user-invocable	false

Command Execution Principles

Security

Never execute user input directly:

• ❌ exec(userInput)
• ❌ shell("rm " + userFile)
• ✅ Use argument lists, not shell string concatenation
• ✅ Validate and sanitize all arguments

Run with minimum permissions:

• Never run commands as root/admin without explicit human approval. If elevated permissions are absolutely required, STOP and request authorization.
• Use least-privilege service accounts

Portability

Use language standard library:

• Avoid shell commands when standard library provides functionality
• Example: Use file I/O APIs instead of cat, cp, mv

Test on all target OS:

• Windows, Linux, macOS have different commands and behaviors
• Use path joining functions (don't concatenate with /)

Error Handling

Check exit codes:

• Non-zero exit code = failure
• Capture and log stderr
• Set timeouts for long-running commands
• Handle "command not found" gracefully

Command Execution Checklist

• Is user input sanitized/validated before use in commands?
• Are arguments passed as lists (not shell string concatenation)?
• Are commands running with minimum necessary permissions?
• Are exit codes checked and errors handled?
• Are timeouts set for long-running commands?
• Is stderr captured and logged?

Related Principles

• Security Mandate @.claude/rules/security-mandate.md
• Security Principles @.claude/rules/security-principles.md