No! It isn't.

my @foo = qw[ a b c d e f ];
my $foo_count = @foo;               # $foo_count is 6
my $foo_last  = $foo[$foo_count];   # There is no $foo[6] so undef
my $real_last = $foo[-1];           # Always works
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A lazier way is:

(split(/\//, $bar))[-1]