Perl Programming/Variables

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In Perl, there are five types of variables: $calars, @rrays, %hashes, &subroutines, and *typeglobals.

[edit] Simple variables

Variables, called scalars, are identified with the $ character, and can contain nearly any type of data. For example:

$my_variable = 3;                              # integers
$my_variable = 3.1415926;                      # floating point
$my_variable = 3.402823669209384634633e+38;    # exponents
$my_variable = $another_variable + 1;          # mathematical operation
$my_variable = 'Can contain text';             # strings
$my_variable = \$another_variable;             # scalar reference
$my_variable = \@array_variable;               # array reference
 
print $my_variable;

[edit] Arrays

Arrays in Perl use the @ character to identify themselves.

@my_array = (1, 2, 3, 4, 5, 6, 7, 8, 9, 10);    # numeric list
@my_array = (1 .. 10);                          # same as above
@my_array = ('John', 'Paul', 'George', 'Ringo') # strings
@my_array = qw/John Paul George Ringo/          # the same - one-word strings, with less typing
@my_array = qw/red blue 1 green 5/;             # mixed types
@my_array = (\@Array1, \@Array2, \@Array3);     # array of arrays
 
foreach my $Item (@my_array) {
    print "Next item is $Item \n";
}

However, when you deal with just one element of the array (using square brackets so it's not confused), then that element of the array is considered a scalar which takes the $ sigil:

$my_array[0] = 1;

As in the C programming language, the number of the first element is 0 (although as with all things in Perl, it's possible to change this if you want). Array subscripts can also use variables:

$my_array[$MyNumber] = 1;

[edit] Associative arrays

Associative arrays, or "hashes," use the % character to identify themselves.

%my_hash = ('key1' => 'value1', 'key2' => 'value2');

When using the => the left side is assumed to be quoted. For long lists, lining up keys and values aids readability.

%my_hash = (
    key1    => 'value1',
    key2    => 'value2',
    key3    => 'value3',
);

However, when you deal with just one element of the array (using braces), then that element of the array is considered a scalar and takes the $ identifier:

$my_hash{'key1'} = 'value1';

Associative arrays are useful when you want to refer to the items by their names.

[edit] Subroutines

Subroutines are defined by the sub function, and can be called using &, though it is not recommended. Here's an example program that calculates the Fibonnaci sequence:

sub fib {
    my $n = shift;
    return $n if $n < 2;
    return fib( $n - 1 ) + fib( $n - 2 );
}
 
print fib(14);