in subroutines, @_ is the array of arguments passed to the subroutine -- $_ is not related to @_ -- specificly, 
$_ isn't $_[0]

$_[0] is the first element of @_

Compare to $a, @a, and $a[0]

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Does this make sense?

In reply to Re: Passing values in a hash to a subroutine: by Anonymous Monk
in thread Passing values in a hash to a subroutine: by Elihu

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