Question

 foreach (@v) { s/^\s+//; s/\s+$// }
        push @{$data[$x]}, @v;
      }

I'm getting an error : global variable @data requires explicit package name –
Not sure how to add "my" to it.

But I also don't understand this line of code,

• It's pushing the v element into data[x]. But how does the @ work. I understand the {} is used for hash.

Answer 1

my declares lexically-scoped variables. It doesn’t seem appropriate here, since there appear to be no new variables being named, unless @data is new, in which case the my must move:

push @{(my @data)[$x]}, @v;

which is mostly useless as the lexical scope of @data disappears immediately, or more clearly and usefully:

my @data;
push @{$data[$x]}, @v;

where @data is in a slightly larger scope.

---

perlreftut explains @{...}. Without my,

push @{$data[$x]}, @v;

means to take the $xth element of the @data array, treat it as an array reference, and append @v to it.

For example,

my @data = (
    [],          # 0
    ['a'],       # 1
    ['b'],       # 2
    ['c', 'd'],  # 3
);
my $x = 2;
my @v = ('e', 'f');

push @{$data[$x]}, @v;
# @data = (
#     [],               # 0
#     ['a'],            # 1
#     ['b', 'e', 'f'],  # 2
#     ['c', 'd'],       # 3
# );