[Login to see the link] This is not exactly what you are looking for but the source material for the book is in the following git repository:
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There's a chapter in the book for each source file, but Jacob Stopak commented all of the code in the repository so you may not need the book if you can understand his comments. 🙂
5 The C Header File cache.h
6 Read the Index with read-cache.c
7 Initialize Git with init-db.c
8 Stage Files with update-cache.c
9 Create Trees with write-tree.c
10 Commit Changes with commit-tree.c
11 Read from the Repo with read-tree.c
12 View File Contents with cat-file.c
13 Calculate Diffs with show-diff.c
Here's the first 4 chapters of the book:
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