In instances where you may not have typos—those exist?—, etc., you can disable the warning like so: 
{
   no warnings 'once';
   # ...
}

[download]
For now I'd follow the advice of Corion.

In reply to Re: Confused about 'Name "main::whenfound" used only once:' by eff_i_g
in thread Confused about 'Name "main::whenfound" used only once:' by Maze

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