use warnings;
use strict;

my @AoA;

foreach ( <DATA> )
{
    for ( my @i = split( /\s+/ ); $#i >= 0; )
    {
        unless ( defined( $AoA[ $#i ] )          )
               {          $AoA[ $#i ] = [ ];     }

        push @{ $AoA[ $#i ] } , pop( @i );
    };
}

print join( ', ' , @{ $AoA[ 0 ] } ) , "\n";

__DATA__
1 2 3
4 5 6
7 8 9
A B C
D E F
G H I
J K L
M N O
P Q R
S T U
V W X
Y Z !