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Perl 101 (Part 2) - Of Variables And Operators

Now that you've got the basics of the language down, this secondarticle in the series teaches you about Perl's variables and operators, andalso introduces you to conditional expressions.

TABLE OF CONTENTS:
  1. Perl 101 (Part 2) - Of Variables And Operators
  2. Q
  3. 2 2 ...
  4. ... Or Two Plus Two
  5. Comparing Apples And Oranges
  6. Decisions! Decisions!
  7. Handling The Gray Areas
  8. Miscellaneous Notes
By: Vikram Vaswani and Harish Kamath, (c) Melonfire
Rating: starstarstarstarstar / 6
June 01, 2000

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In the first part of this tutorial, we introduced you to the basics of Perl, Austin Powers-style. This week, we're going to get down and dirty with variables and operators, and also provide you with a brief introduction to Perl's conditional expressions.

To begin with, let's answer a very basic question for all those of you unfamiliar with programming jargon: what's a variable when it's at home?

A variable is the fundamental building block of any programming languages. Think of a variable as a container which can be used to store data; this data is used in different places in your Perl program. A variable can store both numeric and non-numeric data, and the contents of a variable can be altered during program execution. Finally, variables can be compared with each other, and you - the programmer - can write program code that performs specific actions on the basis of this comparison.

Every language has different types of variables - however, for the moment, we're going to concentrate on the simplest type, referred to in Perl as "scalar variables". A scalar variable can hold any type of value - integer, text string, floating-point number - and is usually preceded by a dollar sign.

The manner in which scalar variables are assigned values should be clear from the following example:
#!/usr/bin/perl
# a simple scalar variable
$name = "mud";
# and an example of how to use it
print ("My name is ", $name);

And here's what the output of that program looks like:
My name is mud

Really?! We feel for you...

It shouldn't be too hard to see what happened here - the scalar variable $name was assigned the text value "mud", and this value was then printed to the console via the print() statement.

Although assigning values to a scalar variable is extremely simple - as you've just seen - there are a few things that you should keep in mind here:
  • A scalar variable name must be preceded by a dollar [$] sign - for example, $name, $id and the like. This helps differentiate between scalar variables and arrays or hashes, which are the other types of variables supported by Perl.
  • Every scalar variable name must begin with a letter, optionally followed by more letters or numbers - for example, $a, $data123, $i_am_god
  • The maximum length of a scalar variable name is 255 characters; however, if you use a name that long, you need therapy!
  • Case is important when referring to scalar variables - in Perl, a $cigar is definitely not a $CIGAR!
  • It's always a good idea to give your variables names that make sense and are immediately recognizable - it's easy to tell what $gross_income refers to, but not that easy to identify $ginc.
  • Unlike other programming languages, a scalar variable in Perl can store both integers and floating-point numbers [also known as decimals]. This added flexibility is just one of the many nice things about Perl.
Here's another program, this one illustrating how variables can be used to store and manipulate numbers.
#!/usr/bin/perl
# declare a variable
$number = 19;
print ($number, " times 1 is ", $number,"\n");
print ($number, " times 2 is ", $number * 2, "\n");
print ($number, " times 3 is ", $number * 3, "\n");
print ($number, " times 4 is ", $number * 4, "\n");
print ($number, " times 5 is ", $number * 5, "\n");

And here's what the output looks like:
19 times 1 is 19
19 times 2 is 38
19 times 3 is 57
19 times 4 is 76
19 times 5 is 95



 
 
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