[perl] abs_path не понимаю

#!/usr/bin/perl

use strict;
use warnings;
use Cwd;
use Cwd 'abs_path';

my $path = $ARGV[0];
my $r = abs_path($path);
print "$r\n";

# ./1.pl /usr/lib/ololo
/usr/lib/ololo

# ./1.pl /usr/lib/ololo/
Use of uninitialized value $r in concatenation (.) or string at ./1.pl line 10.

# ./1.pl /usr/lib/ololo/1
Use of uninitialized value $r in concatenation (.) or string at ./1.pl line 10.