# 1. non-destructive
    my $var = $_[0];                      # first element of @_
    my @list = @_;                        # complete @_
    # 2. destructive
    my $var = shift;                      # first element gets removed
+ from @_
    my ($foo, $bar) = map { shift } 1,2;  # two elements get removed f
+rom @_
[download]

If @_ needs to be intact for subsequent calls, as in

sub foo {
    my $foo = $_[0];
    my $quux = baz(@_)
    return $foo ^= $quux;
}
[download]

the non-destructive methods are used. Also, as the variables passed in via the vector @_ are references aliases to the thingies the caller provided, the non-destructive way is often used to do in-place transformations.

Otherwise, it just doesn't matter. Since after setting up the variables in the sub's scope @_ isn't looked at anymore, arguments may be shifted or not. In these cases saying $var = shift or $var = $_[0] does the same for the sub, although the impact on @_ is different.

So, saying $var = shift and @list = @_ is just caring about copying, but done that, not caring about @_ any more.

Using the arguments in a sub without prior assignment (i.e. without copying, as $_[0] .. $_[$#_]) modifies the thingies in the caller.

--shmem

<update> changed reference to alias as per tye's post </update>

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}