Just two more things to be aware of.  It's usually better to specify the module name as a string ("Sybase::DBlib")¹, otherwise you'd get a "Bareword ... not allowed" error when running under "use strict".

Second, the "use if ..." condition is tested at compile time. In this particular case with $ARGV[0] this is not a problem, because the variable is initialized early on. But if you use some other variable, you might need to wrap its assigment in a BEGIN {...} block...

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¹ only with "use if", that is — with plain "use", in contrast, a bareword is needed.