xlsfinfo can be used for finding out what worksheet names exist in the file. For OOXML files you can do with the OCT interface (specify "oct" for the REQINTF parameter). For other Excel file types you need MS-Excel for Windows (or later version) and the windows package (specify "com" for REQINTF), and/or Apache POI and Java support (then the input parameter REQINTF should be specified with a value of 'poi' (case-insensitive) and -obviously- the complete POI interface must have been installed).