my %uid = (
    123 => 456,
    ...
);
my %gid = (
    500 => 1024,
    ...
);
open my $process_handle, "find $topdir -type f |";
while ( <$process_handle> ) {
    chop; # or chomp
    my($uid, $gid) = (stat)[4,5];
    chown $uid{$uid}, $gid{$gid}, $_
        if $uid{$uid} && $gid{$gid};
}