Linux itself is not a copy of
Unix because one can argue it simply conforms to the
POSIX standard. However, how about the
GNU Coreutils which contains utilities like
rm, etc...? Is there any standard defining the names of these basic utilities and their behaviors? If not, can we say it was copied from
All these utilities and their behaviors are defined in the POSIX standard.
GNU is acronym of GNU's Not UNIX. GNU created to make Unix-compatible system without any use of Unix code, not ideas and command names.
Coreutils is a consolidation of three utilities that used to be provided separately. Fileutils,textutils and shellutils all of which were provided by GNU. Shellutils provides the commands you cite, ls, cd, though I think rm comes from fileutils iirc. Going back a little further GNU was a project started by Richard Stallman to provide a free alternative to UNIX, and so mostly of the core set of commands you find on all UNICES were also available through GNU. Unfortunately for Richard, the Linux kernel got more attention than his unfinished HURD kernel and so the most popular UNIX or UNIX like system on the planet is a hybrid of the Linux Kernel supported and supporting the GNU set of utilities.
I was around in the linux world when this transition was occuring, and it made life a little difficult at first when one wanted to use different compiletime configurations for each one, but ce le vie. For a while there, my name was part of coreutils. I gave uname the ability to distinguish different Intel and Intel-Compatible processors from one another rather than just an i386. Until then all intel based unix systems were just high speed i386s and didn't take advantage of the different extended instruction sets available. That who CPU recognition block has now been completely replaced with something a lot more elegant and a modern, and you can only find my name as a historical reference in some antiquated patches that are still floating around, but still it was a cool feather in my cap for a few years and helped me land my first real IT job.
We may casually call the operating system Linux, but that's a truncation of what it really is which is GNU Linux or GNU/Linux.