title: How to add a directory to the PKG_CONFIG_PATH environment variable?
body: <p>Im new using Ubuntu, the problem is that i want to install opencv, then i want to see the version of the installed program using this sentence</p>
  
  <pre><code>pkg-config --modversion opencv
  </code></pre>
  
  <p>Then the terminal shows me this type of "error"</p>
  
  <pre><code>Package opencv was not found in the pkg-config search path.
  Perhaps you should add the directory containing `opencv.pc'
  to the PKG_CONFIG_PATH environment variable
  No package 'opencv' found
  </code></pre>
  
  <p>I tried to do everything and it doesnt work, someone knows how to fix it?</p>