Command Not Found even after changing path variable

Using heroku for deployment while learning Rails with the Ruby On Rails tutorial by Michael Hartl, on Ubuntu 11.04 Natty Narwhal. I installed it using

sudo gem install heroku

and the commands seemed to run fine for that session in the terminal. The next time I went to work, I tried the command "heroku open" and I was told "heroku: command not found".开发者_JAVA技巧 Looking at some of the answers to similar problems here, it seemed the answer was to run

gem enviroment

which returned the following:

RubyGems Environment:
- RUBYGEMS VERSION: 1.3.7
- RUBY VERSION: 1.8.7 (2010-08-16 patchlevel 302) [i686-linux]
- INSTALLATION DIRECTORY: /var/lib/gems/1.8
- RUBY EXECUTABLE: /usr/bin/ruby1.8
- EXECUTABLE DIRECTORY: /var/lib/gems/1.8/bin
- RUBYGEMS PLATFORMS:
- ruby
- x86-linux
- GEM PATHS:
 - /var/lib/gems/1.8
 - /home/richard/.gem/ruby/1.8
- GEM CONFIGURATION:
 - :update_sources => true
 - :verbose => true
 - :benchmark => false
 - :backtrace => false
 - :bulk_threshold => 1000
- REMOTE SOURCES:
 - http://rubygems.org/

I then ran

$ export PATH=$PATH:/var/lib/gems/1.8/bin

which seemed to fix the problem. However, the next time I tried to run heroku in the terminal, I was told "command not found" again! Running the "export PATH=$PATH" command seems to fix the problem every time, but I would rather I didn't have to run this command everytime I want to use heroku. Is there any permanent solution to the problem?

---

If you're using bash as your shell, then add that export line to .bash_profile in your home directory. The equivalent for zsh is .zshrc, and other shells have their own files to automatically load for every shell session.