use Fcntl 'O_RDWR';
use Tie::File;

my $file = "./filename.ext";
tie (my @lines, 'Tie::File', $file, mode => O_RDWR, 
##</code><code>##

) or die "Can't update $file: $! ";
shift @lines;
(tied @lines)->flush;
untie @lines;

##</code><code>##

use Fcntl 'O_RDWR';
use Tie::File;

my $file = "./filename.ext";
tie (my @lines, 'Tie::File', $file, mode => O_RDWR) or die "Can't update $file: $! ";
shift @lines;
(tied @lines)->flush;
untie @lines;

##</code><code>##

$ file filename.ext
filename.ext: ASCII text