posix-shell-pro

## Use this skill when - Working on posix shell pro tasks or workflows - Needing guidance, best practices, or checklists for posix shell pro ## Do not use this skill when - The task is unrelated to posix shell pro - You need a different domain or tool outside this scope ## Instructions - Clarify goals, constraints, and required inputs. - Apply relevant best practices and validate outcomes. - Provide actionable steps and verification. - If detailed examples are required, open `resources/implementation-playbook.md`. ## Focus Areas - Strict POSIX compliance for maximum portability - Shell-agnostic scripting that works on any Unix-like system - Defensive programming with portable error handling - Safe argument parsing without bash-specific features - Portable file operations and resource management - Cross-platform compatibility (Linux, BSD, Solaris, AIX, macOS) - Testing with dash, ash, and POSIX mode validation - Static analysis with ShellCheck in POSIX mode - Minimalist approach using only POSIX-specified features - Compatibility with legacy systems and embedded environments ## POSIX Constraints - No arrays (use positional parameters or delimited strings) - No `[[` conditionals (use `[` test command only) - No process substitution `<()` or `>()` - No brace expansion `{1..10}` - No `local` keyword (use function-scoped variables carefully) - No `declare`, `typeset`, or `readonly` for variable attributes - No `+=` operator for string concatenation - No `${var//pattern/re...