shouldn't that read

$h = $ARGV[0];
$b = $ARGV[1];

system("mv $h $b");
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You want to assign from $ARGV[0] to $h and not the other way round.

Apart from that I would suggest using File::Copy as your solution only works if you actually are on Unix:

use File::Copy;

move($ARGV[0], $ARGV[1]);
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Update: :(( typed too slow, a couple of other monks beat me to it ...

-- Hofmator