That and much more is already supported in Spreadsheet::Read's xlscat utility. See -s option to alter the default | to whatever you like, and -c and -m for CSV output:

usage: xlscat [-s <sep>] [-L] [-u] [ Selection ] file.xls
              [-c | -m]       [-u] [ Selection ] file.xls
               -i                  [ -S sheets ] file.xls
    Generic options:
       -v[#]       Set verbose level (xlscat)
       -d[#]       Set debug   level (Spreadsheet::Read)
       -u          Use unformatted values
       --noclip    Do not strip empty sheets and
                   trailing empty rows and columns
    Input CSV:
       --in-sep=c  Set input sep_char for CSV
    Output Text (default):
       -s <sep>    Use separator <sep>. Default '|', \n allowed
       -L          Line up the columns
    Output Index only:
       -i          Show sheet names and size only
    Output CSV:
       -c          Output CSV, separator = ','
       -m          Output CSV, separator = ';'
    Selection:
       -S <sheets> Only print sheets <sheets>. 'all' is a valid set
                   Default only prints the first sheet
       -R <rows>   Only print rows    <rows>. Default is 'all'
       -C <cols>   Only print columns <cols>. Default is 'all'
       -F <flds>   Only fields <flds> e.g. -FA3,B16
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