$line =~ s/(\$\w+->{\w+})/"$1 or ''"/eeg;
# or
$line =~ s/(\$\w+->{\w+})/eval "$1" or ''/eg;
# or my favorite
$line =~ s/(\$\w+->{\w+})/eval "$1" or 
           print(STDERR "$1 is not defined\n"), ''/eg;