UNIX can be frustrating for beginners. At first, it can seem as if UNIX is picky and will object to everything you type. The next sections cover the common errors that beginners make to help you avoid them.
UNIX is Case-Sensitive
Case-sensitive means that you must use the same upper- and lowercase letters in a filename or command. If you use the wrong case, you cannot access the file or command.
Under UNIX, the following filenames would refer to different files:
acme aCme acMe acmE ACME acME aCMe AcMe AcmE Acme aCME AcME
All these files could be in use in a directory at the same time because, under UNIX, it matters whether the letter is in uppercase or lowercase. ...