How to use the command 'git apply' (with examples)

Git is a distributed version control system that allows developers to track changes in code and collaborate effectively. The git apply command is used to apply patches to files in a Git repository without creating a commit. It is an alternative to the git am command, which applies patches and creates commits. This article provides a detailed explanation of various use cases of the git apply command along with the code examples, motivations, explanations, and example outputs.

Use case 1: Print messages about the patched files

Code:

git apply --verbose path/to/file

Motivation: By using the --verbose option, the git apply command prints detailed information about the files that have been patched. This can be useful for developers who want to keep track of the changes being applied.

Explanation:

• git apply: The command to apply patches to files in the Git repository.
• --verbose: An option that provides detailed output about the applied patches.

Example output:

Checking patch path/to/file...
Applied patch path/to/file

Use case 2: Apply and add the patched files to the index

Code:

git apply --index path/to/file

Motivation: In some cases, developers might want to apply patches and immediately add the patched files to the Git index. This allows them to stage the changes for the next commit.

Explanation:

• git apply: The command to apply patches to files in the Git repository.
• --index: An option that adds the patched files to the Git index.

Example output: No output will be displayed unless an error occurs during patch application.

Use case 3: Apply a remote patch file

Code:

curl -L https://example.com/file.patch | git apply

Motivation: The git apply command can also be used to apply patch files from remote sources such as websites. This allows developers to apply patches directly from the internet.

Explanation:

• curl -L https://example.com/file.patch: A command to download the patch file from a remote location and pipe it to the git apply command.
• |: The pipe operator redirects the output of the first command to the input of the second command.

Example output: No output will be displayed unless an error occurs during patch application.

Use case 4: Output diffstat for the input and apply the patch

Code:

git apply --stat --apply path/to/file

Motivation: The --stat option of the git apply command can be used to display statistics about the applied patch, including the number of inserted and deleted lines. This can help developers understand the impact of the patch on the codebase.

Explanation:

• git apply: The command to apply patches to files in the Git repository.
• --stat: An option that displays diffstat information about the applied patch.
• --apply: An option to indicate that the patch should be applied.

Example output:

path/to/file | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

Use case 5: Apply the patch in reverse

Code:

git apply --reverse path/to/file

Motivation: The --reverse option of the git apply command allows developers to reverse the changes made by a patch. This can be useful when it is necessary to undo the changes introduced by a patch.

Explanation:

• git apply: The command to apply patches to files in the Git repository.
• --reverse: An option that applies the patch in reverse, effectively undoing the changes made by the patch.

Example output: No output will be displayed unless an error occurs during patch application.

Use case 6: Store the patch result in the index without modifying the working tree

Code:

git apply --cache path/to/file

Motivation: The --cache option of the git apply command allows developers to store the result of the patch in the index without modifying the working tree. This can be useful when it is desired to stage the changes without affecting the current state of the files.

Explanation:

• git apply: The command to apply patches to files in the Git repository.
• --cache: An option that stores the patch result in the index without modifying the working tree.

Example output: No output will be displayed unless an error occurs during patch application.

Conclusion

The git apply command is a powerful tool for applying patches to files in a Git repository. It provides various options to control the behavior of patch application and allows developers to stage changes without creating a commit. By understanding the different use cases and options of the git apply command, developers can effectively manage and apply patches in their Git workflow.