pasted from CGI.pm - a Perl5 CGI Library - The HTML Shortcuts Section

When processing an uploaded file, CGI.pm creates a temporary file on your hard disk and passes you a file handle to that file. After you are finished with the file handle, CGI.pm unlinks (deletes) the temporary file. If you need to you can access the temporary file directly. Its name is stored inside the CGI object's "private" data, and you can access it by passing the file name to the tmpFileName() method:

$filename = $query->param('uploaded_file');
       $tmpfilename = $query->tmpFileName($filename);
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