if(exists($foo{bar}) and exists($foo{bar}{baz})) {
  print "\$foo{bar}{baz} exists\n";
}
[download]

by doing soemthing like this:

my @levels = qw/bar baz/; 
foreach(@levels) {

$_ = 'exists('.$_.')';
}
my $code = '('.join(' and ', @levels).')';
#$code is now: (exists($foo{bar}) and exists($foo{bar}{baz})
if (eval $code) {
 #do whatever
}
[download]

Note that the order of @levels is important.