Java™ Application Development on Linux - Dator

26Chapter 1An Embarrassment of Riches: The Linux Environmentyou’ve got it debugged. Assuming we put those commands into a file calledmyscript, here’s a sample run:$ myscriptUI_Button.java ==> GUI_Button.javaUI_Plovar.java ==> GUI_Plovar.javaUI_Screen.java ==> GUI_Screen.javaUI_Tofal.java ==> GUI_Tofal.javaUI_Unsov.java ==> GUI_Unsov.java...$Imagine having to rename 200 files. Now imagine having to do that witha point-and-click interface. It could take you all morning. With our shell script,it will be done in seconds.We can’t hope to cover all that we’d like to about shell scripting. Perhapswe have been able to whet your appetite. There are lots of books on the subjectof shell programming. We’ve listed a few at the end of this chapter.1.3.11 The tar and zip CommandsThe tar and zip commands allow you to pack data into an archive or extract itback. They provide lossless data compression (unlike some image compressionalgorithms) so that you get back out exactly what you put in, but it can takeup less space when archived. 8 Therefore tar and zip are often used for databackup, archival, and network transmission.There are three basic actions that you can take with tar, and you canspecify which action you want with a single letter 9 in the arguments on thecommand line. You can either8. Well, technically, tar doesn’t compress the data in the file, but it does provide a certainamount of “compression” by cutting off the tail ends of blocks of data; for example, a file of37 bytes in its own file takes up 4K of disk space since disk blocks are allocated in “chunks”(not the technical term). When you tar together a whole bunch of files, those extra tail-endempty bytes are not used (except in the final block of the TAR file). So, for example, 10 filesof 400 bytes could be packed into a single 4K file, instead of the 40K bytes they would occupyon the filesystem. So, while tar won’t compress the data inside the file (and thus is quiteassuredly “lossless”) it does result in a smaller file.9. Linux option strings always start with a “-”, right? Yes, except for tar. It seems there is alwaysan exception to every rule. The newer versions of tar allow the leading minus sign, but can alsowork without it, for historical compatibility reasons. Early versions of UNIX only had single