A Practical Guide for better understanding Git Diff

Introduction

In this guide, We will get basic understanding of various git diff options. We will see:

Diff between Local Working Dir and Staging area
Diff between Local Working Dir and Git repo (Latest commit)
Diff between Staging area and Git repo (Latest commit)

And,

Diff for particular file
Diff between commit ids

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Git diff

Diff between local working dir and staging area

If you do only git diff, it will show difference in files between staging and unstaged (local file).

Example, if you do changes in two files: t1, t2 And, do a git add t1 on one file only. Then, git diff will show difference for t2 only.

# after changing files t1, t2
$ git add t1
$ git status
Changes to be committed:
  (use "git reset HEAD <file>..." to unstage)

	modified:   t1

Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

	modified:   t2

Now, if I run git diff

$ git diff

diff --git a/t2 b/t2
index 45b983b..7c7e506 100644
--- a/t2
+++ b/t2
@@ -1 +1 @@
-hi
+hi hi hi

It shows difference of the file which has not been staged yet.

Diff between local working dir and Git repo(latest)

git diff HEAD

In the above example, I had modified two files: t1, t2. I staged only one file: t1.

$ git diff HEAD

diff --git a/t1 b/t1
index 45b983b..880d1a7 100644
--- a/t1
+++ b/t1
@@ -1 +1,3 @@
 hi
+hi
+hi
diff --git a/t2 b/t2
index 45b983b..7c7e506 100644
--- a/t2
+++ b/t2
@@ -1 +1 @@
-hi
+hi hi hi

Note, I get the diff of all the files on local dir vs the actual remote git repo.

Diff between Staging area and Git repo(latest)

In the above example, I had modified two files: t1, t2. I staged only one file: t1.

$ git diff --staged HEAD

diff --git a/t1 b/t1

index 45b983b..880d1a7 100644
--- a/t1
+++ b/t1
@@ -1 +1,3 @@
 hi
+hi
+hi

I’m only getting diff on the file I did staged.

Diff for only particular file

By default, git diff returns the diff of all the files changed/added. If you want to get diff of one particular file, do this:

git diff -- t2

Diff between Commit Ids

Lets list the commit ids in shorter format.

$ git log --oneline

e7dd2a0 (HEAD -> master, origin/master, origin/HEAD) t2
007675f t1
1a2af9c test
f997108 test
9a5a776 test
85587c6 test1
574c251 test 1

Lets get diff between two commits

$ git diff 574c251 e7dd2a0

## output

diff --git a/test1.txt b/t1
similarity index 100%
rename from test1.txt
rename to t1
diff --git a/t2 b/t2
new file mode 100644
index 0000000..45b983b
--- /dev/null
+++ b/t2
@@ -0,0 +1 @@
+hi
diff --git a/test2.txt b/test2.txt
new file mode 100644
index 0000000..45b983b
--- /dev/null
+++ b/test2.txt
@@ -0,0 +1 @@
+hi

Get the diff between a commit id and latest commit