When deploying your Nikola blog with a post-receive hook keep in mind that you can't just use
Executing this command will result in the following error message.
This behavior is caused by the fact, that git does not use the PWD environment variable but GIT_DIR. Changing the directory does not change GIT_DIR, and therefore a git pull will fail. To get the behavior, you want to set the GIT_DIR environment variable like the following example shows.
Now you can continue to build your blog using Nikola.