Perl Complex Variables

Perl has 3 types, scalar, array and hash. These can be combined to make complex variables.

Unfortunately, the syntax isn't kind.

Defining Scalars, Arrays and Hashes.

$name = 'andrew' ;

# these 2 are the same, qw() is 'syntax sugar'
@names = qw( andrew john peter );
@names = ('andrew', 'john', 'peter');

%age = (
 'andrew' => 20,
 'peter'  => 30,
 'paul'   => 17,
 );

# note the outside hash uses (
# - but the inside hash uses {

%names = (
 'andrew' => { 
      'age'    => 20, 
      'height' => 1.76,
      },
 'peter'  => { 
      'age'    => 30, 
      'height' => 1.2, 
      'friends'=> ['andrew', 'paul'], 
      }
 );

Scalars

$x =  $names{'andrew'}{'age'};
# now $x = 20 

$names{'andrew'}{'age'} = 35 ;

Arrays

Arrays are a bit more complex - use @{ } to access them and [ ] to set them

@x = @{ $names{'peter'}{'friends'} } ;

$names{'peter'}{'friends'} = [ 'bill', 'john', 'fred' ] ;

Hashes

Hashes are similar, use %{ } to access them and { } to set them

%hash = %{ $names{'andrew'} } ;

$names{'andrew'} = { 'age' => 20, 'height' => 1.76 } ;

Important Gotcha

When using the %hash = %{} and @array = @{} syntax, you are making a reference to the data, NOT a copy of it;

%hash = %{ $names{'andrew'} } ;
# %hash is a reference, change %hash and you change %names, and visa versa

%new_hash = %hash;
# now safe