When you examine a commit, normally what you see is the 'changes made since the previous commit'. This does not mean that a Git commit contains only the changes made since the previous commit. As you recall, a Git commit contains a full snapshot of the working directory. However, tools used to examine commits typically show only the changes, as that is the more informative part.

Git shows changes included in a commit by dynamically calculating the difference between the snapshots stored in the target commit and the parent commit. This is because Git commits store snapshots of the working directory, not changes themselves.

Although each commit represents a copy of the entire working directory, Git uses space efficiently in two main ways:

1. Reuse of unchanged data: If a file hasn’t changed since a previous commit, the commit simply points to the already stored version of that file instead of making another copy. This means only new or changed files take up extra space, while unchanged files are reused.
2. Compression: Git also compresses all the files and data it stores using an algorithm (zlib). So, even the objects that are stored (whether reused or new) take up less disk space because they are saved in a compressed format.

To address a specific commit, you can use its SHA (e.g., e60deaeb2964bf2ebc907b7416efc890c9d4914b). In fact, just the first few characters of the SHA is enough to uniquely address a commit (e.g., e60deae), provided the partial SHA is long enough to uniquely identify the commit (i.e., only one commit has that partial SHA).
Naturally, a commit can be addressed using any ref pointing to it too (e.g., HEAD, master).
Another related technique is to use the <ref>~<n> notation (e.g., HEAD~1) to address the commit that is n commits prior to the commit pointed by <ref> i.e., "start with the commit pointed by <ref> and go back n commits".
A related alternative notation is HEAD~, HEAD~~, HEAD~~~, ... to mean HEAD~1, HEAD~2, HEAD~3 etc.

Git uses the diff format to show file changes in a commit. The diff format was originally developed for Unix. It was later extended with headers and metadata to show changes between file versions and commits. Here is an example diff showing the changes to a file.

diff --git a/fruits.txt b/fruits.txt
index 7d0a594..f84d1c9 100644
--- a/fruits.txt
+++ b/fruits.txt
@@ -1,6 +1,6 @@
-apples
+apples, apricots
 bananas
 cherries
 dragon fruits
-elderberries
 figs
@@ -20,2 +20,3 @@
 oranges
+pears
 raisins
diff --git a/colours.txt b/colours.txt
new file mode 100644
index 0000000..55c8449
--- /dev/null
+++ b/colours.txt
@@ -0,0 +1 @@
+a file for colours

    

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A Git diff can consist of multiple file diffs, one for each changed file. Each file diff can contain one or more hunk i.e., a localised group of changes within the file — including lines added, removed, or left unchanged (included for context).

diff --git a/fruits.txt b/fruits.txt
index 7d0a594..f84d1c9 100644
--- a/fruits.txt
+++ b/fruits.txt

    

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@@ -1,6 +1,6 @@
-apples
+apples, apricots
 bananas
 cherries
 dragon fruits
-elderberries
 figs

    

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@@ -20,2 +20,3 @@
 oranges
+pears
 raisins

    

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diff --git a/colours.txt b/colours.txt
new file mode 100644
index 0000000..55c8449
--- /dev/null
+++ b/colours.txt

    

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@@ -0,0 +1 @@
+a file for colours

    

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HANDS-ON: View specific commits

TargetView contents of specific commits in a repo.

Preparation You can use any repo that has commits e.g., the things repo.

CLI

1 Locate the commits to view, using the revision graph.

git log --oneline --decorate

    

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⤷

 e60deae (HEAD -> master, origin/master) Update fruits list
 f761ea6 Add colours.txt, shapes.txt
 2bedace Add figs to fruits.txt
 d5f91de Add fruits.txt

    

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2 Use the git show command to view specific commits.

git show  # shows the latest commit

    

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⤷

commit e60deaeb2964bf2ebc907b7416efc890c9d4914b (HEAD -> master, origin/master)
Author: damithc <...@...>
Date:   Sat Jun ...

    Update fruits list

diff --git a/fruits.txt b/fruits.txt
index 7d0a594..6d502c3 100644
--- a/fruits.txt
+++ b/fruits.txt
@@ -1,6 +1,6 @@
-apples
+apples, apricots
 bananas
+blueberries
 cherries
 dragon fruits
-elderberries
 figs

    

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To view the parent commit of the latest commit, you can use any of these commands:

git show HEAD~1
git show master~1
git show e60deae  # first few characters of the SHA
git show e60deae.....  # run git log to find the full SHA and specify the full SHA

    

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To view the commit that is two commits before the latest commit, you can use git show HEAD~2 etc.

---

Sourcetree

Click on the commit. The remaining panels (indicated in the image below) will be populated with the details of the commit.

---

done!

git config --global alias.lodg "log --oneline --graph --decorate"

    

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alias gs='git status'
alias glod='git log --oneline --graph --decorate'

    

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