in reply to
difference between @, $
@a is an array, or potentially a set of values, while $a is a scalar, or single value. In this case, $a is being used to hold a reference to an array, but the reference is still a single value. I think you probably intended to assign the array values in list context, rather than just adding a reference:
@a = ['1','2','3','4']; ### NO
@a = ('1','2','3','4'); ### YES
print $_ for @a; ### Prints 1234
print $a[0]; ### Prints 1
### Note that you use $ and not @ when referring to a
### single item in the array
$a = ['1','2','3','4'];
print $_ for @$a; ### Prints 1234
print $a->[0]; ### Prints 1
### The -> is used when it's a reference to an array