Pass a reference to the array, either explicitly,

sub array_fn {
    my @array = @{+shift};
    # ...
}
array_fn(\@foo);
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or else implicitly with a prototype,

sub array_fn (\@) {
    my $array = shift;
    # do things to @$array
}
array_fn(@foo);
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The prototype version is generally reserved for subs which will modify their argument array.