How to Show Changes in Commit in Git: A Complete Guide for Developers

As a full-stack developer, understanding Git commit diffs is an indispensable skill for collaborating on software projects. Reviewing line changes within commits helps identify exactly what was added, enabling robust code reviews, undoing changes, pinpointing issues, and more.

In this comprehensive guide, we‘ll delve into various methods to uncover commit changes using Git. Both beginning users and experienced developers can gain new insights for incorporating commit diffing into their workflows.

Why Reviewing Commit Diffs Matters

Before diving into the diffing tools, let‘s discuss why inspecting commits changes is valuable in the first place:

1. Conduct Code Reviews – The most common use case for commit diffs is during code review. Diffs enable reviewers to ensure quality standards and provide precise feedback on each introduction.

2. Revert Functionality – If a commit introduces a regression bug, developers can easily revert it by applying the changes in reverse.

3. Understand Code Evolution – Commit diffs provide a change log of all development activity – perfect for getting familiar with large, unfamiliar codebases.

According to Stack Overflow‘s 2022 survey, nearly 90% of professional developers now use Git:

With Git becoming ubiquitous, fluency in leveraging commits can be a deciding factor in developing modern applications efficiently.

Now let‘s explore the tools available.

Using git show to Display Commit Changes

git show <commit> prints the full commit details, including all file diffs representing the changes:

git show 7668736 

For example, here a bug fix was committed:

commit 7668736dd11ca25fa17558a481c069d928143f8
Author: John <john@example.com>
Date:   Thu Feb 16 11:22:43 2023 -0500

    Fix cart item subtotal calculation  

diff --git a/src/store/cart.js b/src/store/cart.js

- function calculateTotal(items) {
+ function calculateSubtotal(items) {
     return items.reduce((total, item) => {
-      return total + item.price; 
+      return total + (item.price * item.quantity);
     }, 0);
   }

Reviewing this diff during code review clearly shows the logic fix applied to calculateSubtotal().

Later if issues emerge, engineers can pinpoint this commit and revert it if necessary.

Getting Granular With git diff

While git show reveals full commit details, git diff focuses exclusively on comparing two commits:

git diff <commit1> <commit2>

For example, let‘s analyze the diffs when a new search feature was added:

git diff 7668736 7628a32^!

Output:

+ function initSearch() {
+   // index products  
+ }

+ export function searchProducts(query) {
+  let results = [];
+  
+  // perform search logic
+  return results;  
+ }

The + lines indicate exactly what was added in the commit range. If any bugs arise with search, developers know where to look.

Getting Stats with git diff --stat

To scope out which files were changed and the number of modifications in a commit, append the --stat option:

git diff --stat 7668736

Output:

src/store/cart.js | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

This provides a high-level overview before investigating the full diffs. Evaluating these stats across projects can reveal insightful trends too.

Here is an example chart of additions and deletions across an e-commerce site:

Noticing large chunks of deletions or modifications might prompt further inspection into those components.

Visualizing History With gitk

For visualizing commit sequence and diffs, gitk provides a handy UI:

Clicking through commits shows associated diffs inline. This graphical interface complements terminal workflows.

Leveraging GitHub/GitLab Diff Views

The major Git hosting providers including GitHub and GitLab conveniently display diffs when browsing commits:

The web UI allows quickly leafing through file changes within a series of commits. The interface also supports commenting on specific lines, enabling collaborative code reviews.

Best Practices For Informative Commits

To get the most of out reviewing commit diffs, it‘s best to keep commits focused and descriptive. Here are some key practices:

• Make commits small and self-contained when possible
• Follow conventions for clear subject lines summarizing logic
• Use imperative mood e.g "Fix bug" instead of "fixed" or "fixes"
• Explain rationale for why a change was made in the description
• Keep unrelated changes in separate commits

Ensuring quality commit messages helps peers comprehend the diffs better.

Integrating Diffs into CI Pipelines

In addition to manual analysis, commit diffs can be highly valuable for powering Continuous Integration (CI) pipelines.

For example, diffs can be used to:

• Run focused test suites – only test files/units changed in a commit
• Lint changed files – run linters on modified files rather than whole codebase
• Notice high-risk changes – flag edits in protected files/directories
• Derive changelog entries – pull commit messages automatically

Analyzing diffs within automated builds multiplies the benefits.

Here is an example workflow integrating commit diffs:

Key Takeaways

• Inspecting commit diffs facilitates code reviews, reverting changes, and understanding code progression
• git show reveals full commit metadata and associated file changes
• git diff focuses specifically on the line diffs between two commits
• --stat displays a summary of changes rather than full diffs
• GUI tools like gitk and GitHub provide graphical commit browsing
• Well-structured commits with summaries optimize the diffing experience
• Automate analyzing diffs in CI pipelines for faster testing and awareness

I hope this guide has provided both new and seasoned developers more ideas on leveraging commit diffs to aid development. Git‘s builtin diffing capabilities unlock incredibly helpful workflows.

Now go show those commit changes!