Diff

The diff command displays changes in different elements of the working environment: files, directories, commits, and even branches. In other words, diff shows what changed for one or several elements in a repository.

Syntax

The syntax for comparing data changes in a repository using diff is:

  git diff

Examples

There are various ways in which git diff can be used.

1. git diff

Used as it is, the command shows the difference between the working directory and the staging area.

Suppose the initial version of the file scene.txt below has already been committed.

COBBYTO
In a dream, brain activity will be roughly thirty times higher than usual. The effect is increased by entering a dream within that dream.

ARIANEA
How long should each level take?

The file scene.txt is modified as follows and the changes are saved in the working directory.

COBBYTO
In a dream, brain activity will be roughly thirty times higher than usual. The effect is increased by entering a dream within that dream.

ARIANEA
How long?

COBBYTO
According to my calculations, the time span is approximately three days at the top layer, three months one layer down, and six years a level after.

ARIANEA
Who would want to live in an illusory world for six years?

Using git diff in the terminal will produce the following output:

$ git diff
diff --git a/scene.txt b/scene.txt
index c16c37f..c680bb4 100644
--- a/scene.txt
+++ b/scene.txt
@@ -2,4 +2,10 @@ COBBYTO
 In a dream, brain activity will be roughly thirty times higher than usual. The effect is increased by entering a dream within that dream.

 ARIANEA
-How long?
\ No newline at end of file
+How long?
+
+COBBYTO
+According to my calculations, the time span is approximately three days at the top layer, three months one layer down, and six years a level after.
+
+ARIANEA
+Who would want to live in an illusory world for six years?
\ No newline at end of file

With only one file tracked, using git diff is the same as using git diff scene.txt

2. git diff –cached

git diff --cached displays the changes between the staging area and the last commit (i.e., changes between what is staged but not yet committed).

If git diff --cached is run in the terminal, no output is produced. This is expected because nothing has been added to the staging area yet. Therefore, there’s no status change between the latter and the last commit. This can be verified by running git status.

$ git status
On branch master
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:   scene.txt

no changes added to commit (use "git add" and/or "git commit -a")

Adding scene.txt to the staging area and running git diff --cached in the terminal yield the following:

$ git diff --cached
diff --git a/scene.txt b/scene.txt
index c16c37f..c680bb4 100644
--- a/scene.txt
+++ b/scene.txt
@@ -2,4 +2,10 @@ COBBYTO
 In a dream, brain activity will be roughly thirty times higher than usual. The effect is increased by entering a dream within that dream.

 ARIANEA
-How long?
\ No newline at end of file
+How long?
+
+COBBYTO
+According to my calculations, the time span is approximately three days at the top layer, three months one layer down, and six years a level after.
+
+ARIANEA
+Who would want to live in an illusory world for six years?
\ No newline at end of file

The output is the same as the output for git diff in the previous section because the changes saved have been added to the staging area. Additionally, if git diff is run in the terminal, no output is produced.