I would have used '-1' as the subscript. Would have. As of about 5 minutes ago I changed my mind as to the appropriateness of using -1 as a subscript.

Consider the following blocks...

$[ = -4;
@a = (qw(a b c d e f g h i j));
print $a[-1], "\n";
print $a[$#a], "\n";
__DATA__
d
j
[download]

and

$[ = 0;
@a = (qw(a b c d e f g h i j));
print $a[-1], "\n";
print $a[$#a], "\n";
__DATA__
j
j
[download]

There is some DWIMmery with the -1 option that could cause problems, especially if you are working on old, or someone else's code of unknown usage or localization of the $[ variable. And yes, I have read the disclaimers not to use the $[ variable in the fine manual. I didn't say that I would use the variable. :-)

Update: This is perl, v5.8.8 built for PA-RISC2.0

Comparison

Update #2: Comparison of perl binary available on this machine:

for x in 100 1 0 -1 -6 -7 -11 -12 -99; do
    perl -le "\$[=$x; my @ra=qw(a b c d e f); print \$[, ': -1:' , \$r
+a[-1], ': $#: ', \$ra[\$#ra]"
done
[download]

• This is perl, version 5.005_02 built for PA-RISC1.1

  100: -1: f: $#: f
  1: -1: f: $#: f
  0: -1: f: $#: f
  -1: -1: f: $#: f
  -6: -1: f: $#: f
  -7: -1: f: $#: e
  -11: -1: f: $#: a
  -12: -1: f: $#: 
  -99: -1: f: $#:
  [download]

This is perl, v5.8.8 built for PA-RISC2.0

100: -1: f: $#: f
1: -1: f: $#: f
0: -1: f: $#: f
-1: -1: a: $#: f
-6: -1: f: $#: f
-7: -1: : $#: e
-11: -1: : $#: a
-12: -1: : $#: 
-99: -1: : $#:
[download]

Conclusion: Don't use $[ as anything other than 0 (as presented by a couple of other monks so far.