Unix vs Linux: 6 Key Differences Every Developer Should Know

The article clarifies that while Linux is a Unix-like system derived from Unix, significant differences exist that affect portability and development practices.

1. Bash Is Not the Standard Shell

On all Unix systems the default shell is sh, not bash. POSIX defines the language for sh. Many Linux distributions symlink sh to bash, allowing bash-specific features that are not portable. Developers should consult the POSIX standard when in doubt.

2. Unix Does Not Have Long Options

Unix commands traditionally use short options (single dash, e.g., grep -c). Long options (double dash, e.g., grep --count) are a GNU extension. BSD systems and the standard getopts utility and getopt C function support only short options.

3. Make Differs from GNU Make

POSIX make is more limited than GNU make, notably lacking logical OR and conditional operators. A common workaround is to move logic into a configure script that generates a secondary Makefile included in the main one. BSD make syntax differs entirely from GNU; however, macOS and Linux both provide GNU make, so GNU features are safe when targeting only those platforms.

4. The C Compiler Is Not Necessarily GCC

In Makefiles, reference the C compiler via $(CC) and the C++ compiler via $(CXX). Most BSD systems now default to Clang and may not provide a gcc executable. Outside Makefiles, the portable commands cc and c++ work on all systems.

5. GNU Is Not Linux

GNU interfaces are not guaranteed on every Linux distribution. For example, Alpine Linux uses musl libc and BusyBox instead of GNU core utilities. Even when targeting Linux only, using portable interfaces is advisable.

6. Unix vs UNIX (Trademark)

UNIX

(all caps) is a trademark certified by The Open Group. macOS is a prominent certified UNIX system that conforms to all UNIX specifications. Most Unix-like systems (including BSD) and GNU tools strive to follow the standards, but only certified systems may use the UNIX mark.

Original author: Mohamed Akram. Translated by CSDN.