Perl 101 (Part 2) - Of Variables And Operators (
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Now that you've got the basics of the language down, this second
article in the series teaches you about Perl's variables and operators, and
also introduces you to conditional expressions.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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