title: How to repair jekyll and bundle installation
body: <p>The command <code>bundle exec jekyll serve</code> stopped to work correctly on my system, and leads now to this error:</p>
  <pre><code>bash: /usr/local/bin/bundle: /usr/bin/ruby2.5: bad interpreter: No such file or directory
  </code></pre>
  <p>I don't know how it happened, but gem tells me that jekyll and bundle are not installed, when actually they are present in a different path:</p>
  <pre><code>$ which gem
  /usr/bin/gem
  
  $ which ruby
  /usr/bin/ruby
  
  $ which bundler
  /usr/local/bin/bundler
  
  $ which jekyll
  /usr/local/bin/jekyll
  
  $ lsb_release -a
  Distributor ID: Ubuntu
  Description:    Ubuntu 20.04.1 LTS
  Release:    20.04
  Codename:   focal
  
  $ gem --version
  3.1.2
  
  $ ruby --version
  ruby 2.7.0p0 (2019-12-25 revision 647ee6f091) [x86_64-linux-gnu]
  </code></pre>
  <p>I don't know how to undo that. I looked around and there are several ways to repair this (export a path, reinstall ruby), but I'm unsure which way is the less likely to break my system more.</p>