#!/usr/bin/perl

use strict;
use warnings;
use autodie;

my @files = qw( 1.txt 2.txt 3.txt );
my @matrix;

for my $file ( @files ) {
    open my $fh, '<', $file;
    push @matrix, [ map $_+0, <$fh> ];
}

for my $i ( 0 .. $#matrix ) {
    my $row = $matrix[$i];
    print "$i: @$row\n";
}