How to generate git diff patch?

To understand the process involved in it, we need to first understand the terminologies that is being used in the git.

Suppose you have committed your code in Git repository. Now when you select the particular commit, then you will see something like this

TK-34164 e2e test cases added
Commit: 96f17e85e5b76cff8a6a0332c4f22d10aca3aec6 [96f17e8]
Parents: 56a575c5b8
Author: Abhishek Kumar 
Date: 3 January 2017 at 18:52:06 IST
Labels: HEAD -> feature/TK-34164-configure-robot-framework-into

Here at line #1 is custom message for the commit, after that at line #2 you see a commit-id which is 40 characters long hexadecimal string (SHA-1) and it's short version in square bracket which is 7 characters long. 

SHA-1 (Secure Hash Algorithm 1) produces a 160-bit (20-byte) hash value known as a message digest. A SHA-1 hash value is typically rendered as a hexadecimal number, 40 digits long.

This commit-id is 160-bit SHA-1 hash, uniquely represents the new, post-commit state of the repository. 

Now we need to get the changes of our code, that is known as diff. We can get the diff by using this command.

For single commit

git diff-tree -p {commit} > {filename}

Here, {commit} is a single short commit-id and {filename} is a patch file that could be like patch.diff

For multiple commit

git diff-tree -p {from-commit}..{to-commit} > {filename}

Here, {from-commit}..{to-commit} is a range of short commit-id and {filename} is a patch file that could be like patch.diff

So you need to just replace the portion of string with curly bracket with your specific content.

This way you can generate a patch.diff via git program.

In case you want to merge this patch.diff into the repository, then use the following command

git apply patch.diff

That's it!