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functions / ref

(source, CPAN)

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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";
    }