Perl CGI: The Happy Path: Perl Variables

Prepared by Bill Kilgallon, Bill@KilgallonFamily.com

A scalar is just a fancy name for a variable, which can be thought of as a shoebox.

You can put a name on the side of a shoebox, so that you can tell it apart from all the other shoeboxes. This is the scalar or variable name.

You can put a value into a shoebox for safekeeping. You have to tell perl which shoebox you want to put the value into by specifying the shoebox name.

All shoeboxes are empty every time a program starts. When a program ends, all values in shoeboxes are lost.

You can do interesting things to the values in shoeboxes. You can replace them, manipulate them, compare them, and modify them.

If you are using the "use strict;" directive in your program, you must put the word "my" before your first use of any variable. It should not appear with any future uses of that same variable in that same program. If you are not using the "use strict" directive, you are far from the happy path, and probably doomed anyway.

To create a scalar named "count" and set it's value to 10, you would use command "my $count = 10;" the first time. If "$count" had previously been used in the program and had the "my" directive already, it would simply be "$count = 10";

To then add one to the value in this variable, and then store that result back in the same variable, you could use any one of the following directives:
```
$count = $count + 1;
$count += 1;
```

To display a variable, you can use the print command. The arguments supplied to a print command will output when the program executes. If a variable name appears in an argument to a print statement in double quotes, the contents of that variable will be displayed. Arguments supplied to print in single quotes do not show the contents of the variable. For example:
```
my $count = 10;
$count = $count + 30;
print "Count is $count\n";
print 'Count is not $count\n';
```
would output
```
Count is 40
Count is not $count
```

The "\n" at the end of the print argument simply specifies that a carriage return should be added to the shown text. By default, Perl will not include a carriage return and successive lines would run together on one really long line, which looks silly.

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