I guess I should have been less specific!
@$0 is seen as @{ $0 }
The issue isn't limited to $0 following the @: no matter what variable follows it—whether it exists or not—the @ is not interpreted literally. 
$ perl -e 'print "@$$\n";'

$ perl -e 'print "@$undefined_variable\n";'

$ perl -e 'print "@$]\n";'
]
$ perl -e 'print "@$(\n";'
(

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Interestingly, sometimes the entire @$foo seems to be interpreted as a unit, printing nothing, and other times @$ seems to be interpreted as one unit, printing whatever follows it literally. In no case is the @ interpreted literally. And, of course, in all cases preceding the @ with a backslash solves that, and allows the following variable to be interpolated: 
$ perl -e 'print "\@$$\n";'
@24477
$ perl -e 'print "\@$undefined_variable\n";'
@
$ perl -e 'print "\@$]\n";'
@5.030003
$ perl -e 'print "\@$(\n";'
@500 7 10 11 16 18 19 27 35 80 85 100 105 500

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In reply to Re^2: escaping the @ in an interpolating string by raygun
in thread escaping the @ in an interpolating string by raygun

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