qichunren@zhaobak:~> gem install hpricot
ERROR: While executing gem ... (Gem::FilePermissionError)
You don\'t have write permissions into the /opt/ruby-enter
I was getting this error on my shared server through 1and1 hosting.
my solution was adding the --user-install option, which just installs it for your logged in user (which is all you need in a shared server environment)
example; installing sass