A comprehensive guide to Git apply command

Introduction

Git is a highly popular version control system that helps developers to collaborate on projects seamlessly. It is fast, reliable, and secure. However, learning Git can be a bit challenging due to its vastness and complexity. One of the critical Git commands that developers use while working on a project is Git apply. This command helps to apply the changes from one branch to another. In this article, we will go through Git apply command, its usage, and examples.

Git apply command

Git apply command is used to apply a patch from one branch or file to another. A patch is a file that contains the changes that are made to a file or a set of files. You can create a patch using the Git diff command. Git apply command is mainly used when you want to apply changes from a branch that is not your current branch.

In its simplest form, the Git apply command takes a patch file and applies it to the current branch. Here is the syntax of the Git apply command:

$ git apply <path/to/patch>

You can also apply a patch from a URL or directly from the clipboard.

$ git apply <(curl -s <link/to/patch>)

$ git apply -

The last command above will apply the patch from the clipboard.

In general, the Git apply command works in three modes:

1. Full apply mode
2. Index apply mode
3. Check mode

We will discuss each mode in more detail below.

Full apply mode

Full apply mode is the default mode of Git apply. This mode applies the changes directly to the files in your working directory. If the files do not exist, Git creates them. You can use the –index option to apply changes to the index instead of the working directory.

$ git apply --index <path/to/patch>

Index apply mode

Index apply mode applies the changes to the index but not the working directory. This mode is useful when you want to review the changes before applying them to the working directory.

$ git apply --cached <path/to/patch>

Check mode

Check mode is used to check if a patch can be applied without actually applying it. This mode is useful when you want to test a patch before applying it to your codebase.

$ git apply --check <path/to/patch>

Applying a patch to a specific file

You can also apply a patch to a specific file by providing its path along with the patch file.

$ git apply <patch/file> <path/to/file>

Applying a patch from a different branch

To apply a patch from a branch other than the current branch, you need to specify the branch name along with the patch path.

$ git apply <path/to/patch> --3way <branch/name>

The –3way option above tells Git to apply the patch using a three-way merge strategy. This strategy combines the changes from two branches and integrates them into a new branch.

Applying multiple patches

You can apply multiple patches by providing their paths one after the other.

$ git apply <patch/file1> <patch/file2> <patch/file3>

Reversing a patch

To reverse a patch, you need to use the Git revert command.

$ git revert <commit-id>

The above command creates a new commit that reverts the changes made by the specified commit.

Example usage

Suppose you have made changes to a file and created a patch file named ‘changes.patch.’ You want to apply these changes to a different branch named ‘dev.’ Here are the commands that you need to run:

$ git checkout dev
$ git apply changes.patch --3way

The above commands will apply the patch to the ‘dev’ branch using a three-way merge strategy.

Conclusion

Git apply command is a powerful feature that allows you to apply changes from one branch or file to another. It is particularly useful when you want to apply changes from a branch other than the current branch. In this article, we have gone through the usage of Git apply command and discussed its various modes. We have also provided examples to demonstrate the usage of this command. With this knowledge, you can now confidently use the Git apply command to apply patches to your codebase.