Here are the steps I followed to download, install, and run EpubCheck 3.0.1 on my epub.
1. To download EpubCheck 3.0.1, navigate to https://github.com/IDPF/epubcheck/releases using Safari and click on epubcheck-3.0.1.zip button.
2. Click Show downloads in Safari.
3. Right-click on epubcheck-3.0.1 and select Show in Finder. The finder window will show the downloaded and unzipped directory, usually /Users/myname/Downloads/epubcheck-3.0.1.
4. Open the Terminal application. Type the following command to change directory:
If you get a pop up with the message:
To open “java,” you need a Java SE 6 runtime. Would you like to install one now?
Click Install button.
When it’s done installing, click OK on the Installing one item window.
6. Now ‘java -version’ should output something like this:
java version “1.6.0_65”
Java(TM) SE Runtime Environment (build 1.6.0_65-b14-462-11M4609)
Java HotSpot(TM) 64-Bit Server VM (build 20.65-b04-462, mixed mode)
7. Now run:
java -jar epubcheck-3.0.1.jar /Users/username/Documents/mybook.epub > mybook.epub.errors 2>&1
8. A file called mybook.epub.errors will have been created in your current directory (/Users/myname/Downloads/epubcheck-3.0.1).
9. You can view the file by running:
Press ‘q’ to exit.
10. Alternatively, you may right-click the file in a Finder window and select Open with→Other. Select TextEdit from the Applications directory. You will see a window with the contents of mybook.epub.errors.