As already menionned by davido, if you pass two arrays to a sub, they get flattened into one bigger list. So you need to pass array references to the sub.

As an example, this is one possible way to pass array references to a sub and to use them within the sub.

my @a = (1, 2, 3);
my @b = (5 .. 7);
process(\@a, \@b); # pass array references to the sub

sub process {
    my ($a1ref, $a2ref); # retrieve the params
    my @array1 = @{$a1ref); # dereference $a1ref inti an array
    my @array2 = @{$a2ref);
    # ... process @array1 and @array2
    # ...
}
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Update: removed underscores from $a1_ref and $a2_ref variable in initialization to make variable names consistent with the following code lines.