When I do - CD .. instead of cd ..it gives me error saying -  CD: command not foundWhy is the terminal case sensitive when it comes to linux commands? I mean you should be able to execute the command either with all uppercase or all lowercase characters.  I know it is due to some reason, but I am just curious.
Why is the terminal case-sensitive?
shell;user interface
Ultimately, it was an arbitrary choice made by the creators of Unix over four decades ago now. They could have chosen to make things case-insensitive like the creators of MS-DOS did a decade later, but that has its disadvantages, too.It's too deeply embedded in *ix culture to change now. The case sensitive filesystem issue brought up by eppesuig is only part of it. Mac OS X systems — which are Unix-based — typically have case-insensitive file systems, so on such systems commands external to the shell are in fact treated case-insensitively. But, builtins like cd remain case-sensitive.Even with a case-insensitive filesystem, the history of things conspires against your wishes, Hussain. If I type ls on my Mac, I get a colorized directory listing. If I type LS instead, /bin/ls still runs, but the listing isn't colorized because the alias that adds the -C flag is case-sensitive.Best just get used to it. If you can, learn to like it.