use strict;
use warnings;
use Cwd;
use Win32::OLE;

my $ext = ".xls";
my $newext = ".csv";

my $Excel=Win32::OLE->new('Excel.Application');
$Excel->{Visible}=1;
$Excel->{DisplayAlerts}=1;	#Set to 0 when the code is working, but keep at 1 while debugging.

my $dir = getcwd;
$dir =~ s/\//\\\\/g;		#Sort out the slashes and backslashes
opendir(DIR, $dir) or die "can't opendir $dir: $!"; #Cookbook recipe 9.5
while (defined(my $file = readdir(DIR))) {
     if ((!-d $file) and (substr($file, -length($ext)) eq $ext)) {	#Someone WILL call a directory something.xls. I have the scars.
		my $Book = $Excel->Workbooks->Open("$dir\\\\$file") or die "Can't open file $dir\\\\$file"; 
		my $sheet = $Book -> Worksheets(1);
		$sheet -> Range ('A:A') -> {NumberFormat} = "000";
			
			#The next line is pretty explicit to try to make it clear what's going on.
		$Book->SaveAs({Filename     => $dir . "\\\\" . substr($file, 0, length($file) - length($ext)) . $newext, 
					   FileFormat   => 6, #xlCSV, 
					   CreateBackup => 0});
		$Book->Close;
	}
}
closedir(DIR);
$Excel->Quit;