From last:

last cannot be used to exit a block that returns a value such as eval {}, sub {}, or do {}, and should not be used to exit a grep() or map() operation.

Note that a block by itself is semantically identical to a loop that executes once. Thus last can be used to effect an early exit out of such a block.

So, last doesn’t work in a do { ... } until (...); loop. But — put the whole construct inside a block, and last now works fine:

#! perl
use strict;
use warnings;

my $n = 42;

{
    do
    {
        printf "n = %d\n", $n--;
        last if $n == 37;

    } until ($n <= 0);
}

print "Past the loop\n";
[download]

Output:

 0:22 >perl 878_Tutorial.pl
n = 42
n = 41
n = 40
n = 39
n = 38
Past the loop

 0:22 >
[download]

Hope that helps,