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       ref EXPR

       ref     Returns a true value if EXPR is a reference, false
               otherwise.  If EXPR is not specified, `$_' will be
               used.  The value returned depends on the type of
               thing the reference is a reference to.  Builtin
               types include:

                   SCALAR
                   ARRAY
                   HASH
                   CODE
                   REF
                   GLOB
                   LVALUE

               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($r) eq "HASH") {
                       print "r is a reference to a hash.\n";
                   }
                   unless (ref($r)) {
                       print "r is not a reference at all.\n";
                   }
                   if (UNIVERSAL::isa($r, "HASH")) {  # for subclassing
                       print "r is a reference to something that isa hash.\n";
                   }

               See also the perlref manpage.


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