POSIX stands for Portable Operating System Interface..
the unix is a form of group in operating system
Linux is a Unix-like system. This means that it is inspired or influenced by Unix in some shape or form (Linux started off from Minix), but it is not directly derived from Unix. However, BSD is based on Unix, and macOS is indirectly Unix-based because of its mixed heritage with BSD.
internet Operating System
GNU is operating system
It means operating system
internet Operating System
All modern day computers have some form of operating system.
Microsoft Disc Operating System
Windows Vista
Some of your options are as follows: Open Solaris. It is based on Sun's Solaris Unix operating system. You can get it from http://opensolaris.org/os/ FreeBSD livecd http://livecd.sourceforge.net/ However, if your only goal is to learn shell scripting all the Linux/Unix variants use the same shells (usually some version of bash, sh, csh, tcsh, or zsh). The bash shell is the same if ran on Linux, Unix, or even Windows.
Disk Operating System -DOS
Uniplexed