How to Use the Command 'git diff-tree' (with examples)

The git diff-tree command is a powerful tool within the Git version control system. It allows users to compare two tree objects, presenting the differences between them in terms of content and mode changes. This command is particularly useful for developers and anyone needing to track changes between directories or two points in their project’s history. Its various options enable users to customize the output to suit their specific needs.

Use case 1: Compare two tree objects

Code:

git diff-tree tree-ish1 tree-ish2

Motivation:

Comparing two tree objects is a common task when you want to understand what has changed between two versions of your entire project directory. It is especially helpful in scenarios such as reviewing changes before a major release or ensuring that refactoring doesn’t alter the expected file structure or content inadvertently.

Explanation:

• git diff-tree: This is the command invoking the comparison of tree objects.
• tree-ish1 and tree-ish2: These placeholders represent two different commits or tree objects you wish to compare. In Git, a “tree” object is a snapshot of the working directory.

Example Output:

The command will list the files that have been modified, added, or deleted between the two tree objects. You might see output similar to:

:100644 100644 bcd123 abc678 M file.txt
:100644 100644 cde234 def789 R rename.txt

Use case 2: Show changes between two specific commits

Code:

git diff-tree -r commit1 commit2

Motivation:

When you need to audit changes between two specific commits, the recursive option -r is invaluable. This can be useful for pinpointing changes introduced by a specific feature branch or verifying the cumulative changes before merging into the main branch.

Explanation:

• -r: This option recursively compares the content of subdirectories.
• commit1 and commit2: These are the specific commit hashes or names that you wish to compare, providing a powerful way to step through change history at a granular level.

Example Output:

The command will produce a detailed list of changes with subdirectory contents, which may look like:

:100644 100644 abcd1234 5678efgh M src/file1.java
:100644 100644 bcde5678 uvw9ijk0 A src/newfile.cpp

Use case 3: Display changes in patch format

Code:

git diff-tree -p tree-ish1 tree-ish2

Motivation:

Viewing changes in patch format is particularly useful when you need a line-by-line understanding of what was altered between two trees. This is often vital in code review processes where granular detail is required to evaluate the impact and correctness of the changes.

Explanation:

• -p or --patch: This flag outputs differences in the more granular “patch” format, showing actual lines added or removed.
• tree-ish1 and tree-ish2: These are the two tree objects to be compared.

Example Output:

The output will include not only which files changed but also a detailed patch showing the exact lines added and removed, such as:

diff --git a/file.txt b/file.txt
index 83adbf3..f7dd13b 100644
--- a/file.txt
+++ b/file.txt
@@ -1,4 +1,4 @@
-Hello world
+Hello Git world

Use case 4: Filter changes by a specific path

Code:

git diff-tree tree-ish1 tree-ish2 -- path/to/file_or_directory

Motivation:

Sometimes, you need to concentrate on changes in a specific part of the project, such as a critical configuration file or a core library. Filtering changes by path enables developers to maintain focus, reducing the noise from unrelated changes.

Explanation:

• tree-ish1 and tree-ish2: These specify the tree objects for comparison.
• -- path/to/file_or_directory: This option filters the output to show only changes within the specified path.

Example Output:

You’d receive output indicating changes only in the specified path:

:100644 100644 ef12345 gh45678 M path/to/file_or_directory/config.yaml

Conclusion

The git diff-tree command is a versatile utility in the Git suite, offering various options to refine and interrogate differences between tree objects. Through examples like comparing two entire directories, showing detailed patch information, and filtering changes to specific paths, git diff-tree proves to be an indispensable tool for both meticulous code inspection and general version control maintenance.