You need to handle the case when comparing a shorter array with a longer one:

#! perl -slw
use strict;

my @un_sorted = ([3,4,23,4,5],[3,4,56,2,4],[2,3,43,5,3],[2,3,43,6],[3,
+4]);

print join "\n", map{ join ',', @$_ } sort {
    for( 0 .. ( $#{$a} < $#{$b} ? $#{$b} : $#{$a} ) ) {
        return ( $a->[$_] || 0 ) <=> ( $b->[$_] || 0 ) || next
    }
} @un_sorted;
__END__
P:\test>before
Use of uninitialized value in numeric comparison (<=>) at P:\test\junk
+.pl line 10.
2,3,43,5,3
2,3,43,6
3,4
3,4,23,4,5
3,4,56,2,4

P:\test>after
2,3,43,5,3
2,3,43,6
3,4
3,4,23,4,5
3,4,56,2,4
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