You need to choose y-1 divisions in your set of objects.

For your example, that would be:

for my $p0 (1     .. 5-1) {
for my $p1 ($p0+1 .. 5-1) {
    print(
        substr('12345', 0, $p0),
        "|",
        substr('12345', $p0, $p1-$p0),
        "|",
        substr('12345', $p1, 5-$p1),
        "\n",
    );
}}
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The general case requires y-1 nested loops. When you have a variable number of nested loop, Algorithm::Loops's NestedLoops is great:

use Algorithm::Loops qw( NestedLoops );

my $num_objects    = 5;
my $num_containers = 3;

my $str = join('', 1..$num_objects);

NestedLoops(
    [
        [ 1 .. $num_objects-1 ],
        (sub { [ $_[-1]+1 .. $num_objects-1 ] }) x ($num_containers-2)
    ],
    sub {
        my $str = $str;
        substr($str, $_, 0, '|') for reverse @_;
        print("$str\n");
    },
);
[download]

1|2|345
1|23|45
1|234|5
12|3|45
12|34|5
123|4|5
[download]