Git in Depth

A real Git

Git is a key-value store. A file is hashed using the SHA-1 algorithm when it's added to a commit. This hash is then used as a key name for the folder and used to store the file.

Git has Porcelain and Plumbing commands

• Porcelain Commands (easy to remember)
  • example: git add, status, commit, stash, etc
• Plumbing Commands (get access to Git internals)
  • example: git hash-object, cat-file, ls-files, rev-parse, ls-remote, etc

hash-object

The git hash-object command hashes the file contents.

git hash-object <filename>
# example
git hash-object hello

As you can see, the key is made up of the first two characters of the hash. The contents of this file (hello) will be stored in this hash file 492f47831b16c8217339fcb1449345b424c72fcb.

To see the hash file contents, you have to use git cat-file command.

cat-file

The git cat-file command will display the contents of the hash file by using the hash value.

git cat-file -p <object-hash>
# example
git cat-file -p 492f47831b16c8217339fcb1449345b424c72fcb # pretty prints the contents

Git Object Contents

There are three types of folders in the object folder.

1. commit
   • A commit is simply just a commit hash.
2. tree
   • It's a folder associated with the repository on your file system.
3. blob
   • It's just a piece of data.
   • For example, the file that hashed (hello) is called a blob.