my $test="my_variable_name"; #imagine this is a hash key
my $default_value="the value I set"; #while this is the hash value

my %hash = ($test => \$default_value);

print "the value of \$$test = ${$hash{$test}}\n";
${$hash{$test}} = "A new value";
print "the value of \$$test = ${$hash{$test}}\n";