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deepmind.google·6d ago
AI Engineering
Hacker News·Jun 28·5 min read
POSIX Is Not a Shell
TL;DR
Many developers mistakenly equate POSIX with a specific shell, leading to portability issues. POSIX is a specification, while various shells like bash and dash implement it differently.
✦ Why It Matters
Engineers should ensure their scripts are tested across multiple shells to guarantee portability.
Key Takeaways
- Always test scripts in multiple shells for compatibility.
- Understand the differences between POSIX and specific shell implementations.
- Use simple commands to verify behavior across environments.
- Document shell-specific features when writing scripts.
Full Summary
POSIX, or Portable Operating System Interface, is a set of standards that defines how operating systems should behave, particularly in terms of command-line interfaces. However, it is not a shell itself; instead, it is implemented by various shells such as bash, dash, and ksh, each with unique features and limitations.
For instance, a simple command may yield different outputs depending on the shell used, as demonstrated with a one-line script that behaves differently in bash compared to dash. This inconsistency can lead to scripts that work in one environment failing in another, complicating the goal of portability.
Developers need to be aware of these differences to write more robust scripts that function across multiple systems. Understanding the specific shell being used and its adherence to POSIX can help mitigate these issues.