Comparing changes with git diff

git diff is a multi-use Git command that when executed runs a diff function on Git data sources.

Diffing is a function that takes two input data sets and outputs the changes between them. git diff is a multi-use Git command that when executed runs a diff function on Git data sources. These data sources can be commits, branches, files and more. This document will discuss common invocations of git diff and diffing work flow patterns. The git diff command is often used along with git status and git log to analyze the current state of a Git repo.

Highlighting changes

  1. git diff --color-words git diff also has a special mode for highlighting changes with much better granularity: ‐‐color-words. This mode tokenizes added and removed lines by whitespace and then diffs those.
  2. git diff-highlight If you clone the git source, you’ll find a sub-directory called contrib. It contains a bunch of git-related tools and other interesting bits and pieces that haven’t yet been promoted to git core. One of these is a Perl script called diff-highlight. Diff-highlight pairs up matching lines of diff output and highlights sub-word fragments that have changed.

Diffing binary files In addition to the text file utilities we have thus far demonstrated, git diff can be run on binary files. Unfortunately, the default output is not very helpful.

Comparing files: git diff file The git diff command can be passed an explicit file path option. When a file path is passed to git diff the diff operation will be scoped to the specified file. The below examples demonstrate this usage.

git diff HEAD ./path/to/file This example is scoped to ./path/to/file when invoked, it will compare the specific changes in the working directory, against the index, showing the changes that are not staged yet. By default git diff will execute the comparison against HEAD. Omitting HEAD in the example above git diff ./path/to/file has the same effect.

git diff --cached ./path/to/file When git diff is invoked with the --cached option the diff will compare the staged changes with the local repository. The --cached option is synonymous with --staged.

Comparing all changes Invoking git diff without a file path will compare changes across the entire repository. The above, file specific examples, can be invoked without the ./path/to/file argument and have the same output results across all files in the local repo.

Changes since last commit By default git diff will show you any uncommitted changes since the last commit.

git diff Comparing files between two different commits git diff can be passed Git refs to commits to diff. Some example refs are, HEAD, tags, and branch names. Every commit in Git has a commit ID which you can get when you execute GIT LOG. You can also pass this commit ID to git diff.

Comparing files from two branches To compare a specific file across branches, pass in the path of the file as the third argument to git diff

git diff main newbranch ./difftest.txt

Summary

This page disscused the Git diffing process and the git diff command. We discussed how to read git diff output and the various data included in the output. Examples were provided on how to alter the git diff output with highlighting and colors. We discussed different diffing strategies such as how to diff files in branches and specific commits. In addition to the git diff command, we also used git log and git checkout.