People have covered the usage of sort, but I think this is also worth mentioning -- when you're swapping two elements, it's not required to use a placeholder. Perl (at least 5.6) allows you to declare anonymous arrays, and abuse them for the greater good.

compare

$placeholder = $date[$n];
$date[$n] = $date[$n2];
$date[$n2] = $placeholder;
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with

($date[$n], $date[$n2])=($date[$n2], $date[$n]);
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each one swaps the contents of $date[$n] and $date[$n2], but there's (IMO) clarity in the second one, as well as a reduction in line count. Here's a small sample to flesh out the idea :

my @foo;
$foo[0]=0;
$foo[1]=1;
print "@foo\n";
($foo[0], $foo[1])=($foo[1], $foo[0]);
print "@foo\n";
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