Git Internals

Git is a content-addressable filesystem where objects are stored as simple key-values, which means you can pass any kind of content into Git and you will get a key that will allow you to retrieve the content.

The key of the object is going to be a 40-character SHA-1 checksum hash (It can be simulated by git hash-object command).

Git objects can be of the below 3 types:

1 - Blob - Zlib Compressed Header and File Content

2 - Tree -  One or more entries, each of which is the SHA-1 hash of a blob or subtree with its associated mode, type, and filename. 

4 - Commit - Top Level Tree, Parent Commit, Author and Commit Description

Git stores the objects inside .git/objects within subdirectories which is named with the first 2 characters of the SHA-1, and the filename is the remaining 38 characters.

git cat-file command is sort of a Swiss army knife for inspecting Git objects.

git cat-file -t [hash] gives the type of the object.

git cat-file -t [hash] will print the content of the object.

While working with git [hash] can be given as only first n chars (depending upon the size of the project) only rather than copying the whole 40 chars.

"Generally, eight to ten characters are more than enough to be unique within a project. One of the largest Git projects, the Linux kernel, is beginning to need 12 characters out of the possible 40 to stay unique." - Source

Source: https://git-scm.com/book/en/v2/Git-Internals-Git-Objects

Getting top contributors of given directory based on commit counts

git log --pretty=format:"%an%x09" dir | sort | uniq -c | sort -nr

git log --pretty option prints the contents of the commit logs in a given format (%an%x09b) for given directory, here %an is placeholder for Author Name and %x09 is placeholder for tab.

Output of first command will be series of author names of commits affecting given directory ordered by date.

Since we are not concerned with order we will just sort the output so that we can easily group the names using uniq -c which along with unique values prints the count.

Now the output is in alphabetical order of Author Names if we want to order by count of commits we can pipe it to sort -nr  where n represents sort by numerical value and r represents sort in reverse order.