What is the meaning of @_ in Perl?

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perldoc perlvar is the first place to check for any special-named Perl variable info.

Quoting:

@_: Within a subroutine the array @_ contains the parameters passed to that subroutine.

More details can be found in perldoc perlsub (Perl subroutines) linked from the perlvar:

Any arguments passed in show up in the
array @_ .

Therefore, if you called a function with two arguments, those
would be stored in $_[0] and $_[1].

The array @_ is a local array, but its
elements are aliases for the actual scalar parameters.
In particular, if
an element $_[0] is updated, the
corresponding argument is updated (or
an error occurs if it is not
updatable).

If an argument is an array
or hash element which did not exist
when the function was called, that
element is created only when (and if)
it is modified or a reference to it is
taken. (Some earlier versions of Perl
created the element whether or not the
element was assigned to.) Assigning to
the whole array @_ removes that
aliasing, and does not update any
arguments.

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