Книга: Fedora™ Unleashed, 2008 edition

A Simple Perl Program

A Simple Perl Program

This section introduces a very simple sample Perl program to get you started using Perl. Although trivial for experienced Perl hackers, a short example is necessary for new users who want to learn more about Perl.

To introduce you to the absolute basics of Perl programming, Listing 25.1 illustrates a simple Perl program that prints a short message.

#!/usr/bin/perl
print "Look at all the camels!n";

Type that in and save it to a file called trivial.pl. Then make the file executable using the chmod command (see the following sidebar) and run it at the command prompt.

The sample program in the listing is a two-line Perl program. Typing in the program and running it (using Perl or making the program executable) shows how to create your first Perl program, a process duplicated by Linux users around the world every day!

The #! line is technically not part of the Perl code at all. The # character indicates that the rest of the screen line is a comment. The comment is a message to the shell, telling it where it should go to find the executable to run this program. The interpreter ignores the comment line.

Exceptions to this practice include when the # character is in a quoted string and when it is being used as the delimiter in a regular expression. Comments are useful to document your scripts, like this:

#!/usr/bin/perl
# a simple example to print a greeting
print "hello theren";

A block of code, such as what might appear inside a loop or a branch of a conditional statement, is indicated with curly braces ({}). For example, here is an infinite loop:

#!/usr/bin/perl
# a block of code to print a greeting forever
while (1) {
 print "hello theren";
};

Perl statements are terminated with a semicolon. A Perl statement can extend over several actual screen lines because Perl is not concerned about whitespace.

The second line of the simple program prints the text enclosed in quotation marks. n is the escape sequence for a newline character.

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