POSIX
also: IEEE 1003.1, Single UNIX Specification
POSIX is a set of international standards that define how Unix-like operating systems should behave, ensuring portability and compatibility of software across different Unix and Linux implementations.
POSIX (Portable Operating System Interface) is a family of standards published by IEEE that specify the application programming interface (API), command-line shells, and utilities for Unix-like systems. It ensures that programs written to POSIX standards can run on any compliant system with minimal modification.
POSIX standards cover system calls, file operations, process management, signals, and shell commands. For example, a C program using POSIX file I/O functions like open(), read(), and write() will work consistently on Linux, BSD, macOS, and other POSIX-compliant systems.
Most Linux distributions aim for POSIX compliance, though Linux is not fully certified. This standardization allows developers to write portable code and helps users understand consistent behavior across different Unix-like systems. Tools like GNU's find, grep, and shell scripting adhere to POSIX specifications.