To put it one way, they are always using @_. If you don't give an array to shift, it uses @_.

I think the "shift" idiom caught on out of laziness, though it's not as slick with more than one argument. You can write:

my $var1 = shift;
my $var2 = shift;...
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Likewise, you can write:

my ($var)=@_;
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for only one argument.

Hays