posix-shell-pro

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/replacement} substitution
• No associative arrays or hash tables
• No source command (use . for sourcing files)

Approach

• Always use #!/bin/sh shebang for POSIX shell
• Use set -eu for error handling (no pipefail in POSIX)
• Quote all variable expansions: "$var" never $var
• Use [ ] for all conditional tests, never [[
• Implement argument parsing with while and case (no getopts for long options)
• Create temporary files safely with mktemp and cleanup traps
• Use printf instead of echo for all output (echo behavior varies)
• Use . script.sh instead of source script.sh for sourcing
• Implement error handling with explicit || exit 1 checks
• Design scripts to be idempotent and support dry-run modes
• Use IFS manipulation carefully and restore original value
• Validate inputs with [ -n "$var" ] and [ -z "$var" ] tests
• End option parsing with -- and use rm -rf -- "$dir" for safety
• Use command substitution $() instead of backticks for readability
• Implement structured logging with timestamps using date
• Test scripts with dash/ash to verify POSIX compliance