If you're just golfing, you can throw away a few characters: 

perl -e 'for$c(sort{$a<=>$b}map/(\d+)$/,<*[0-9]>){++$n==$c||print map"
+$_\n",$n..$c-1;$n=$c}'

[download]

If you want to get rid of the sort, try an array: 

perl -le '@f=map/(\d+)$/,<*[0-9]>;@x[@f]=@f;for(1..$#x){$x[$_]||print}
+'

[download]

Note that if you have a file named '0', it will basically ignore it, but that was the original behavior too. This may eat more memory, but I doubt that will be an issue until you're working with millions of files.

In reply to Re^4: one-line split file sequence checker by kyle
in thread one-line split file sequence checker by wdef2

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