i need to open a template and write data into that. i dont need to open a new .xlsx file. With Spreadsheet::WriteExcelXML is it possible to open a existing file?

You said you need to open a template file. Usually, that implies making a new file based on the template. And writing back to the same file makes the template not a template any more.

But, it is possible to write the data back to the original file:

# open file in read/write mode
open(my $xlshandle, '+<', $xlsfile) or die "Can't open '$xlsfile' for 
+read/write: $!\n";
binmode($xlshandle);
# insert code to read spreadsheet
# reset handle to beginning of file
seek($xlshandle, 0, 0);
my $newxls = Spreadsheet::WriteExcelXML->new($xlshandle); # handle, NO
+T file
# insert code to put updated data into $newxls
$newxls->close();
close($xlshandle);
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BUT, it's much safer to:

my $newxlsfile = $xlsfile . '.new';
my $newxls = Spreadsheet::WriteExcelXML->new($newxlsfile); # file, NOT
+ handle
# insert code to put updated data into $newxls
$newxls->close();
close($xlshandle);
rename($xlsfile, $xlsfile . '.bak');
rename($newxlsfile, $xlsfile);
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You will still get a file with the same name as the original file, AND will have a back up of the original file.

Update: added a call to binmode();