As hdb said, unless you push a reference the original list is lost and there is no way to recover. If you push a reference you don't have a flat list in @biglist though, you have a list of lists which may not be what you want. Maybe the below code will help make it clear

use strict;
use warnings;

my @source = (
        [1, 2, 3],
        [4, 5, 6],
        [7, 8, 9]
);

my @bl1;
print "BL1:\n";
push @bl1,@$_ for @source;
print "$_\n" for @bl1;

my @bl2;
print "BL2:\n";
push @bl2,$_ for @source;
print "@$_\n" for @bl2;
[download]

Output:

BL1:
1
2
3
4
5
6
7
8
9
BL2:
1 2 3
4 5 6
7 8 9
[download]