Beginning Perl Tutorial - Data Types: Hashes

Next: Accessing Hash Elements

The scalar is the building block of all perl data types. A list is just an ordered group of scalars indexed by number. A hash is also a group of scalars, but rather than being ordered by number, it is an unordered list that is indexed by yet another set of scalars called keys. This may seem a bit confusing at first - lets go back to our empty box metaphor. A hash is simply a scattered group of these boxes. Rather than being in a nice, neat line, they're kept in no particular order but the boxes are identified with a special label (a key) on the outside.

The symbol for a hash is the % sign, and the naming conventions remain the same - any combination of letters, numbers and the underscore character, but you may not begin it with a number:

 %myHash
 %special_events
 %disk45 

A hash is also called an associative array, or an array where each value is associated with a corresponding key. Just like a list, you initialize a hash with a set of values inside parentheses. Rather than pushing each element into the list in order, Perl will alternate - setting the first element as a key, and the next as that keys' value, and so on.

 %contactInfo = ('name', 'Bob', 'phone', '111-111-1111'); 

Just like lists, a hash will output everything if you print it as a single item.

 #!/usr/local/bin/perl
 %contactInfo = ('name', 'Bob', 'phone', '111-111-1111');
 print %contactInfo; 

This will output:

 nameBobphone111-111-1111$ 

Since both the keys and the values are simple scalars, the same rules apply - they can be any type of data from integers to strings to more scalars.

Next: Accessing Hash Elements

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