use strict;
use warnings;   # <-- always use strict *and* warnings
use Spreadsheet::WriteExcel;
use Text::CSV_XS;

# Check for valid number of arguments <-- @ARGV in scalar context gives the number of entries in the list
@ARGV == 2 or die "Usage: csv2xls csvfile.txt newfile.xls\n";

# Open the Comma Separated Variable file
open my $fh, "<", $ARGV[0] or die "$ARGV[0]: $!"; # <-- use lexical file handles and 3-arg open

# Create a new Excel workbook
my $workbook  = Spreadsheet::WriteExcel->new ($ARGV[1]);
my $worksheet = $workbook->add_worksheet ();

# Create a new CSV parsing object
my $csv = Text::CSV_XS->new ({ binary => 1, auto_diag => 1 }); # <--- use diagnostics and binary

# Row and column are zero indexed
my $row = 0;

while (my $row = $csv->getline ($fh)) { # <-- safe and fast parsing
    # due to auto_diag there is no reason for error-checking
    my $col = 0;
    $worksheet->write ($row, $col++, $_) for @{$r};
    $row++;
    }