ref
ref - find out the type of thing being referenced
ref EXPR
Returns a TRUE value if EXPR is a reference, FALSE otherwise.  The value
returned depends on the type of thing the reference is a reference to.
Builtin types include:
    REF
    SCALAR
    ARRAY
    HASH
    CODE
    GLOB
If the referenced object has been blessed into a package, then that package 
name is returned instead.  You can think of 
ref()
 as a typeof() operator.
    if (ref($r) eq "HASH") {
        print "r is a reference to an associative array.\n";
    } 
    if (!ref ($r) {
        print "r is not a reference at all.\n";
    } 
See also 
the perlref manpage
.