Running Linux, 5th Edition - Matthias Kalle Dalheimer [419]
Another abstruse feature of Perl is its ability to (more or less) directly access several Unix system calls, including interprocess communications. For example, Perl provides the functions msgctl, msgget, msgsnd, and msgrcv from System V IPC. Perl also supports the BSD socket implementation, allowing communications via TCP/IP directly from a Perl program. No longer is C the exclusive language of networking daemons and clients. A Perl program loaded with IPC features can be very powerful indeed—especially considering that many client/server implementations call for advanced text processing features such as those provided by Perl. It is generally easier to parse protocol commands transmitted between client and server from a Perl script than to write a complex C program to do the work.
As an example, take the well-known SMTP daemon, which handles the sending and receiving of electronic mail. The SMTP protocol uses internal commands such as recv from and mail to to enable the client to communicate with the server. Either the client or the server, or both, can be written in Perl and can have full access to Perl's text- and file-manipulation features as well as the vital socket communication functions.
Perl is a fixture of CGI programming—that is, writing small programs that run on a web server and help web pages become more interactive.
Pros and Cons
One of the features of (some might say "problems with") Perl is the ability to abbreviate—and obfuscate—code considerably. In the first script, we used several common shortcuts. For example, input into the Perl script is read into the variable $_. However, most operations act on the variable $_ by default, so it's usually not necessary to reference $_ by name.
Perl also gives you several ways of doing the same thing, which can, of course, be either a blessing or a curse depending on how you look at it. In Programming Perl, Larry Wall gives the following example of a short program that simply prints its standard input. All the following statements do the same thing:
while ($_ = while ( for (; print while $_ = print while The programmer can use the syntax most appropriate for the situation at hand. Perl is popular, and not just because it is useful. Because Perl provides much in the way of eccentricity, it gives hackers something to play with, so to speak. Perl programmers are constantly outdoing each other with trickier bits of code. Perl lends itself to interesting kludges, neat hacks, and both very good and very bad programming. Unix programmers see it as a challenging medium to work with. Even if you find Perl too baroque for your taste, there is still something to be said for its artistry. The ability to call oneself a "Perl hacker" is a point of pride within the Unix community. * * * [*] Truth be told, Perl also exists now on other systems, such as Windows. Many Windows system administrators claim it to be their preferred language. But it is not even remotely as well known and ubiquitous there as it is on Linux. Java Java is a network-aware, object-oriented language developed by Sun Microsystems. Java originally engendered a lot of excitement in the computing community because it strived to provide a secure language for running applets downloaded from the World Wide Web. The idea was simple: allow web browsers to download Java applets, which run on the client's machine. Many popular Web browsers—including Mozilla and Firefox, the GNOME variant Galeon, and the KDE web browser Konqueror (see Chapter 5)--include support for Java. Furthermore, the Java Developer's Kit and other tools have been ported to Linux. But Java proved suitable for more than applets. It has been used more and more as a general-purpose programming language that offers fewer obstacles for beginners than other languages. Because of its built-in networking libraries,