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Data Types
There are only three types of data in Perl - strings, integers, and floating point numbers.

     strings          "dog"   "cat"  "the_boy"
     integers         1   7  -39   37   43   0
     floating point   1.2  -17.4  83.2  171.006

All Perl variables contain either one, or a combination of more than one, of these basic data types. In performing functions which expect a particular type of data, Perl will automatically adjust the type of data found in a variable to the type needed by the function.

Variable Types
There are three variable types. Each contains one, or a combination of more than one, basic data types.

• Scalar - single string, integer, or floating point number
• Array - list of scalars (each scalar can be a different data type)
• Hash - list of name/value scalar pairs

Variables all begin with one of three characters, depending on the variable type.

• $ - defines a scalar
• @ - defines an array
• % - defines a hash

Scalar
To create a scalar variable, just use it in a line of code and assign it a string, integer, or floating point value. Any scalar can be assigned one of the basic data types.

     $x = "Hello"    # string
     $x = 5          # integer
     $x = 75.3       # floating point number

One a variable is assigned a data type (value), it can later be reassigned a new value of another data type.

Array
An array consists of a list of scalar values and can be created in several ways. Array elements are numbered, with the 0 being the first array elements. Since array elements are scalars, their variable name begins with a $.

     @x = (3,"dog",1.9)    # assign a list of values 
     $x[5]=3               # assigns value to array element number 6
     @newarray = @x[0..3]  # slice of values from existing array

     $size = @x                 # $size is # elements in array
     $last index = $#x          # $lastindex is highest index in array
     $#x = 5                    # truncates array at 5 elements
     @x = ()                    # clears an array
     @x = sort @x               # sort an array
     @x = reverse @x            # reverse an array
     splice (@x, 0, 5)          # remove elements 0-4
     @new = splice (@x, 0, 5)   # @new has the removed elements 0-4
     splice (@x, 2, 1, "dog")   # element 2 replaced with "dog"
     @new = @x[1,4,6]           # @new has only elements 1,4,6
     ($a,$b) = @x               # assigns $a/$b from array

Regardless of the way in which the array is created, each array element can is a single value, consisting of a string, integer, or floating point number. Array elements do not have to be the same data type.

There are two basic ways to walk through an array - using for or foreach loops. The following code show both approaches, along with a few manipulation tips on arrays.

     for ($i=0, $i<10, $i++) { print $myarray[$i] )  # for loop
     foreach $var ($myarray) { print $var }          # foreach loop

Hash
A hash consists of key/value pairs and can be created in several ways

     %x = ("a",1,"b",2,"c",3)         # assign a list of pair values
     %x = ("a"=>1,"b"=>2,"c"=>3)      # comma may be replaced with =>
     $x{"a"}=1  $x{"b"}=2  $x{"c"}=3  # manually add key/value pairs

Regardless of the way in which the hash is created, each hash key and each hash value consist of a single a string, integer, or floating point number. Hash keys do not have to be the same data type. Likewise, hash values do not have to be the same data type.

To walk through a hash, use the keys function to get a list of the hash keys for use in a foreach loop. Or, use the each function, which returns a key/value pair each time it is called. The following code shows both approaches, along with a few manipulation tips on hashes.

     foreach $key (keys %myhash) { print "$key: $hash{$key}\n" }
     while (($key,$value) = each (%myhash)) { print "$key: $value\n" }

     %myhash = ()              # clear a hash
     delete ($myhash{$key})    # remove key/value pair
     if exists $myhash{$key}  # test for existence of a key

If you have any suggestions for additions to these tutorials, please let me know.