Without @{ .. } to derefernce the anonymous array reference, $x would be set to that array reference and $y & $z would be undef.

$line[ 1 ][ 2 ] = [ 3,4,5 ];;

my( $x, $y, $z ) = $line[ 1 ][ 2 ];;

print for $x, $y, $z;;

ARRAY(0x194a9f8)
Use of uninitialized value in print at ...

Use of uninitialized value in print at ...
[download]

With the dereference:

my( $x, $y, $z ) = @{ $line[ 1 ][ 2 ] };;

print for $x, $y, $z;;

3
4
5
[download]