use is compile time. It gets executed regardless of the elsif clause. You could use require: 

elsif($param eq "recv")
{  
  use lib './lib';  
  require Sybase::DBlib;
  Sybase::DBlib->import; # if any imports
}

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In reply to Re^4: Installing Sybase::DBlib problems by shmem
in thread Hello Word\n by wilko

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