no warnings;
use File::Map ':all';

open(my $fh, '+>>', shift) or die; # open/mmap modes must ~~
my $off = $fh->tell;
print $fh join " ", @ARGV;
$fh->flush;

# rotate in place
map_handle(my $mmap, $fh, '+<');
substr($mmap, 0, 0, substr($mmap, $off));