Use the g format instead of f and no further formatting should be required:

    $ perl -e 'printf "%2.4g\n", 23.05'
    23.05
    $ perl -e 'printf "%2.4g\n", 23.00'
    23
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See the sprintf manpage for more details:

    g    The  double  argument  is converted in style f or e
         (or E for G conversions).  
         ...
         Trailing zeros are removed from the fractional part
         of  the result;
         ...
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--
John.