open my $input, '<', 'myfile.txt'
    or die "cannot open myfile.txt: $!";
my @lines = <$input>;

##</code><code>##

my $filename = $ARGV[0]
    or die "Usage: $0 <filename>\n";
open my $input, '<', $filename
  or die "cannot open $filename: $!";
my @lines = <$input>;