# build hash
while() {
...
$hshFoo{$key1}{$key2} = $strFileName;
...
# key1 is a number
# key2 is a sequential number
}

##</code><code>##

    foreach $key (keys %hshFoo) {
        print "  $key => $hshFoo{$key}\n";
    }

##</code><code>##

    foreach $key2 (keys $hshFoo{$key}) {
        ...
    }

Type of arg 1 to keys must be hash (not hash element) at foo.pl line
 341, near "}) "
BEGIN not safe after errors--compilation aborted at foo.pl line 431.