Java™ Application Development on Linux - Dator

14Chapter 1An Embarrassment of Riches: The Linux EnvironmentSecond, the pattern matching is done by the shell, the command interpreter,before the arguments are handed off to the specific command. Any textwith these special characters is replaced, by the shell, with one or more filenamesthat match the pattern. This means that all the other Linux commands (mv,cp, ls, and so on) never see the special characters—they don’t do the patternmatching, the shell does. The shell just hands them a list of filenames.The significance here is that this functionality is available to any and everycommand, including shell scripts and Java programs that you write, with noextra effort on your part. It also means that the syntax for specifying multiplefiles doesn’t change between commands—since the commands don’t implementthat syntax; it’s all taken care of in the shell before they ever see it. Any commandthat can handle multiple filenames on a command line can benefit fromthis shell feature.If you’re familiar with MS-DOS commands, consider the way patternmatching works (or doesn’t work) there. The limited pattern matching youhave available for a dir command in MS-DOS doesn’t work with other commands—unlessthe programmer who wrote that command also implementedthe same pattern matching feature.What are the other special characters for pattern matching with filenames?Two other constructs worth knowing are the question mark and the squarebrackets. The “?” will match any single character.The [...] construct is a bit more complicated. In its simplest form, itmatches any of the characters inside; for example, [abc] matches any of a orb or c. So Version[123].java would match a file called Version2.javabut not those called Version12.java or VersionC.java. The patternVersion*.java would match all of those. The pattern Version?.java wouldmatch all except Version12.java, since it has two characters where the ?matches only one.The brackets can also match a range of characters, as in [a-z] or [0-9].If the first character inside the brackets is a “^” or a “!”, then (think “not”) themeaning is reversed, and it will match anything but those characters. SoVersion[^0-9].java will match VersionC.java but not Version1.java.How would you match a “-”, without it being taken to mean a range? Put itfirst inside the brackets. How would you match a “^” or “!” without it beingunderstood as the “not”? Don’t put it first.Some sequences are so common that a shorthand syntax is included. Someother sequences are not sequential characters and are not easily expressed as arange, so a shorthand is included for those, too. The syntax for these special