即使更改了路径变量，也找不到命令

sudo gem install heroku

gem enviroment

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/

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