Java™ Application Development on Linux - Dator

4Chapter 1An Embarrassment of Riches: The Linux Environmentto do on a Linux system, chances are there is already a command (or a sequenceof commands) which will do it.Finally, we will discuss the extent of our remaining ignorance uponfinishing the chapter.Let us take a moment to explain that last comment. As readers of computerbooks ourselves, we are often frustrated when we discover how lightly a topichas been covered, but particularly so when other parts of the same book arefound to fully explore their topics. When only some parts of a book are thorough,you often don’t know that you don’t know it all. We will introduce somebasic shell concepts and commands here, and we may expand on some of thesein later chapters, but each of our chapters covers topics that could each fill itsown book. Therefore we need to leave out lots of material. We will also let youknow when we have left things out because they are off-topic, or because wedon’t have room. We’ll also try to tell you where to look for the rest of theknowledge. We try to sum this up in a final section of each chapter entitledWhat You Still Don’t Know. But we do have a lot of information to impart,so let’s get going.1.2THE COMMAND LINE:WHAT’S THE BIG DEAL?One of the revolutionary things that UNIX (and thus Linux) did was to separateoperating system commands from the operating system itself. The commandsto display files, show the contents of directories, set permissions, and soon were, in the “olden days,” an integral part of an operating system. UNIXremoved all that from the operating system proper, leaving only a small “kernel”of necessary functionality in the operating system. The rest became executablesthat lived outside of the operating system and could be changed, enhanced, oreven replaced individually by (advanced) users without modifying the operatingsystem. The most significant of these standalone pieces was the commandprocessor itself, called the shell.The shell is the program that takes command-line input, decides whatprogram(s) you are asking to have run, and then runs those programs. Beforethere were Graphical User Interfaces, the shell was the user interface to UNIX.As more developers began working with UNIX, different shells were developedto provide different features for usability. Now there are several shells tochoose from, though the most popular is bash. Some BSD/UNIX die hards