gem install rails doesn't do anything
Try adding -V (upper case) to the end of the install command, if forces the command to be verbose, so you can see things going on. Eg:
sudo gem install rails -V
It'll take quite some time to install rails - there are lot of dependencies and these need to be downloaded - if you have a slow connection, just wait for a bit.
- try to add -V (upper-case) in the parameter, to show more detail of what is downloading
if it still very slow or pending somewhere, it normally indicates a low internet connection to the rubygems.org site(showing in the output window). you can try to update the source of the gem using, by
gem source -r https://rubygems.org/
gem source -a "your new source site"
in my country, after I switch to http://ruby.taobao.org, it only takes 1min to complete the installation.