Using Hard References
Just as there are numerous ways to create references, there are also several ways to use, or dereference, a reference. There is just one overriding principle: Perl does no implicit referencing or dereferencing. When a scalar is holding a reference, it always behaves like a simple scalar. It doesn't magically start being an array or hash or subroutine; you have to tell it explicitly to do so, by dereferencing it.
Using a Variable as a Variable Name
When you encounter a scalar like
$foo, you should be thinking "the scalar value of
foo." That is, there's a
entry in the symbol table, and the
character is a way of looking at whatever scalar value might be
inside. If what's inside is a reference, you can look inside
prepending another funny character. Or looking at it the other way
around, you can replace the literal
$foo with a scalar variable that points to the
actual referent. This is true of any variable type, so not only is
$$foo the scalar value of whatever
$foo refers to, but
the array value of whatever
$bar refers to,
%$glarch is the hash value of whatever
$glarch refers to, and so on. The upshot is that
you can put an extra funny character on the front of any simple
scalar variable to dereference it:
$foo = "three humps"; $scalarref = \$foo; # $scalarref is now a reference to $foo $camel_model = $$scalarref; # $camel_model is now "three humps"
Here are some other dereferences:
$bar = $$scalarref; ...