Thanks Sundialsvc4 for your response. The Spreadsheet module (or one of the other module that I am using) seems to be causing this since it is working fine when I pass in a xls file. Is there some way I can tell the interpreter not to convert these strings when a XLSX file is passed? I tried using

 $str =~ s/TRUE/TRUE/i;
 $str =~ s/FALSE/FALSE/i;
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but that did not help. Thanks, Raj