You're missing a newline on the last line. 
say join "\n", sort { $a <=> $b } keys %{{ map { $_ => 0 } 1..10 }}

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should becan be shortened to 
say for sort { $a <=> $b } keys %{{ map { $_ => 0 } 1..10 }}

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Furthermore, since you assume the list is constant, that can be simplified to 
say for sort { $a <=> $b } 1..10;

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And if you wanted to show that stringification doesn't matter, the following would suffice: 
say for sort { $a <=> $b } map "$_", 1..10;

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In reply to Re^3: Sorting integer value hash keys by ikegami
in thread Sorting integer value hash keys by Anonymous Monk

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