1 1 1
2 2 2
3 3 3
4 4 4
5 5 5

##</code><code>##

   
    #!/usr/bin/perl
    use strict;
    use warnings;
    use diagnostics;

    my $source = "./CONTCAR";
    my $destination = "./OUTPUT";

    open(IN, '<', $source) or die "Couldn't open $source: $!\n";
    open(OUT, '>', $destination) or die "Couldn't write to $destination: $!\n";

    my @data = map [ split ], grep /\S/, <IN>;

foreach (@data) { print "$_\n"; }

    for my $i (0 .. $#data) {
    for my $j (0 .. $#data) {

    next if $i == $j;

    my @coords_i = @{$data[$i]}[0,1,2];
    my @coords_j = @{$data[$j]}[0,1,2];

    printf OUT "%s to %s Distance=%.5f\n",     
        $data[$i][0], $data[$j][0],
        $data[$i][2], $data[$j][2],
        distance(\@coords_i, \@coords_j);
    }
    }

    sub distance {
    my ($aa, $bb) = @_;
    my ($x, $y, $z) = map { $aa->[$_] - $bb->[$_] } 0 .. $#$aa;
    return sqrt(($x - $x)**2 + ($y - $y)**2 + ($z - $z)**2);
    }

    close IN;
    close OUT;

    print "Done.\n";

##</code><code>##

1 to 2 Distance=1.00000
1 to 3 Distance=1.00000
1 to 4 Distance=1.00000
1 to 5 Distance=1.00000
2 to 1 Distance=2.00000
2 to 3 Distance=2.00000
2 to 4 Distance=2.00000
2 to 5 Distance=2.00000
3 to 1 Distance=3.00000
3 to 2 Distance=3.00000
3 to 4 Distance=3.00000
3 to 5 Distance=3.00000
4 to 1 Distance=4.00000
4 to 2 Distance=4.00000
4 to 3 Distance=4.00000
4 to 5 Distance=4.00000
5 to 1 Distance=5.00000
5 to 2 Distance=5.00000
5 to 3 Distance=5.00000
5 to 4 Distance=5.00000