unshift would be bad. That puts "./" at the start of the search list, which means standard module names could be overridden by placing bogus ones in the CWD. 
push @INC,"./";

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Better, but it isn't going to affect use statements, since those are evaluated at compile time. So, 
use lib "./";

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is even better. But best is: 
use lib /some/absolute/path/that/you/control;

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Update: use lib "./" is worse than unshift @INC,"./" because it also prepends "./" to the search path, but does so at compile time, where it can affect other use statements.

In reply to Re^2: use lib './' security safe? by hbo
in thread use lib './' security safe? by SavannahLion

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