It is VERY error prone to use join "," to write CSV from cell data: what if the cell contains a , (or a newline)? Use a CSV module to generate CSV file, like Text::CSV_XS or Text::CSV.

If you use Spreadsheet::Read instead of your set of the three modules, you'd be able to pick a sheet by name. FWIW Spreadsheet::BasicRead requires the other two modules, but you do not have to include those requirements in your script).

For reading xlsx spreadsheets, please use Spreadsheet::ParseXLSX (Spreadsheet::BasicRead (still) uses Spreadsheet::XLSX which is buggy and unmaintained). Any alternative will make you suffer later on. (Spreadsheet::Read uses Spreadsheet::ParseXLSX).

Here is an example for using the modules (tested):

use 5.16.2;
use warnings;

sub usage { die "usage: $0 file.xlsx name [out.csv]\n"; }

my $xls = shift or usage;
my $sht = shift or usage;
my $out = shift // $xls;
   $out =~ s/\.xlsx$/.csv/i;

use Spreadsheet::Read;
use Text::CSV_XS;

my $csv = Text::CSV_XS->new ({ binary => 1, eol => "\r\n", auto_diag =
+> 1 });
open my $fh, ">", $out or die "$out: $!\n";

my $book  = ReadData ($xls) or die "$xls: $!\n";

my $sheet = $book->[$book->[0]{sheet}{$sht}];

foreach my $row (1 .. $sheet->{maxrow}) {
    $csv->print ($fh, [ Spreadsheet::Read::row ($sheet, $row) ]);
    }
close $fh;
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