A variable can't "be a hash or a scalar," but could contain a value called a "reference;" a reference can point to just about any perl entity or data type.

my $val = func();
print "Reference to a HASH!\n" if ref($val) eq "HASH";
print "Reference to a ARRAY!\n" if ref($val) eq "ARRAY";
print "Reference to a SCALAR!\n" if ref($val) eq "SCALAR";
print "A non-reference SCALAR!\n" if not ref($val);
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The above will work if the value returned isn't actually blessed into a package; if that's a possibility, then you might want to check out isa() instead.