Here's how I checked to see if an Excel workbook was open before writing to it with Spreadsheet::WriteExcel. I'm sure there's a better way to do it, but this might get you started:

    # Eval block traps errors in Excel file creation; local 
    # redirection of $SIG{__WARN__} allows error message
    # to be checked to see if the file cannot be created because 
    # it is open.  The redirect is only valid within the enclosing 
    # block.

{
    local $SIG{__WARN__} = sub { $errmsg =  $_[0] };
    eval {$workbook = Spreadsheet::WriteExcel->new($Excelfilename);};

    if ($errmsg) {
        if ($errmsg =~ /may be in use/) {
            print "$Excelfilename is open.\n";
        } else {
            print "Excel file could not be created: $!\n";
        }
    }
}
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