Thanks almut! I was close. Instead of this:

        $ENV{ORACLE_HOME}     = $orahome;
        $ENV{LD_LIBRARY_PATH} = $oralib;
        exec $0, @ARGV;
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I was trying this:

        exec("export ORACLE_HOME=$orahome LD_LIBRARY_PATH=$oralib;
              $0");
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Thanks again, your solution works.