Great Movies... - Perl

Ask a geek to define the term "subroutine", and he'll probably tell you that a subroutine is "a block of statements that can be grouped together as a named entity." Since this definition raises more questions than answers [the primary one being, what on earth are you doing hanging around with geeks in the first place], we'll simplify things by informing you that a subroutine is simply a set of program statements which perform a specific task, and which can be called, or executed, from anywhere in your Perl program.

There are two important reasons why subroutines are a "good thing". First, a subroutine allows you to separate your code into easily identifiable subsections, thereby making it easier to understand and debug. And second, a subroutine makes your program modular by allowing you to write a piece of code once and then re-use it multiple times within the same program.

Let's take a simple example, which demonstrates how to define a sub-routine and call it from different places within your Perl script:

---

#!/usr/bin/perl
# define a subroutine
sub greatest_movie
{
print "Star Wars\n";
}
# main program begins here
print "Question: which is the greatest movie of all time?\n";
# call the subroutine
&greatest_movie;
# ask another question
print "Question: which movie introduced the world to Luke Skywalker, Yoda
and Darth Vader?\n";
# call the subroutine
&greatest_movie;

---

Now run it - you should see something like this:

---

Question: which is the greatest movie of all time?
Star Wars
Question: which movie introduced the world to Luke Skywalker, Yoda and
Darth Vader?
Star Wars

---

Let's take this line by line. The first thing we've done in our Perl program is define a new subroutine with the "sub" keyword; this keyword is followed by the name of the subroutine. All the program code attached to that subroutine is then placed within a pair of curly braces - this program code could contain loops, conditional statements, calls to other subroutines, or calls to other Perl functions. In the example above, our subroutine has been named "greatest_movie", and only contains a call to Perl's print() function.

Here's the typical format for a subroutine:

---

sub subroutine_name
{
statement 1...
statement 2...
.
.
.
statement n...
}

This article copyright Melonfire 2000. All rights reserved.

>>> More Perl Programming Articles          >>> More By Vikram Vaswani and Harish Kamath, (c) Melonfire

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