先做乙個實驗：
chia@edogawachia-sphinx:~/mygit$ cat readme.txt
this is a readme file
created by e.chia 2018/02/06
modified by e.chia 1st time
chia@edogawachia-sphinx:~/mygit$ git status
位於分支 master
無檔案要提交，乾淨的工作區
chia@edogawachia-sphinx:~/mygit$ sudo vim readme.txt
chia@edogawachia-sphinx:~/mygit$ cat readme.txt
this is a readme file
created by e.chia 2018/02/06
modified by e.chia 1st time
add this to show staged version
chia@edogawachia-sphinx:~/mygit$ sudo git add 'readme.txt'
chia@edogawachia-sphinx:~/mygit$ git status
位於分支 master
要提交的變更：
（使用 "git reset head 檔案》..." 以取消暫存）
修改： readme.txt
chia@edogawachia-sphinx:~/mygit$ sudo vim readme.txt
chia@edogawachia-sphinx:~/mygit$ cat readme.txt
this is a readme file
created by e.chia 2018/02/06
modified by e.chia 1st time
add this to show staged version
add this to show working directory version這樣三個區域的版本都不一樣了，branch中的最短，stage暫存區的有一句add this to show staged version，工作區的多一句 add this to show working directory version。
下面測試各種 diff 的用法：
chia@edogawachia-sphinx:~/mygit$ git diff
diff --git a/readme.txt b/readme.txt
index 3e42036..e24b3e0 100644
--- a/readme.txt
+++ b/readme.txt
@@ -2,3 +2,4 @@ this is a readme file
created by e.chia 2018/02/06
modified by e.chia 1st time
add this to show staged version
+add this to show working directory version
chia@edogawachia-sphinx:~/mygit$ git diff --cached
diff --git a/readme.txt b/readme.txt
index d995350..3e42036 100644
--- a/readme.txt
+++ b/readme.txt
@@ -1,3 +1,4 @@
this is a readme file
created by e.chia 2018/02/06
modified by e.chia 1st time
+add this to show staged version
chia@edogawachia-sphinx:~/mygit$ git diff --staged
diff --git a/readme.txt b/readme.txt
index d995350..3e42036 100644
--- a/readme.txt
+++ b/readme.txt
@@ -1,3 +1,4 @@
this is a readme file
created by e.chia 2018/02/06
modified by e.chia 1st time
+add this to show staged version
chia@edogawachia-sphinx:~/mygit$ git diff head
diff --git a/readme.txt b/readme.txt
index d995350..e24b3e0 100644
--- a/readme.txt
+++ b/readme.txt
@@ -1,3 +1,5 @@
this is a readme file
created by e.chia 2018/02/06
modified by e.chia 1st time
+add this to show staged version
+add this to show working directory version
chia@edogawachia-sphinx:~/mygit$ git diff head -- readme.txt
diff --git a/readme.txt b/readme.txt
index d995350..e24b3e0 100644
--- a/readme.txt
+++ b/readme.txt
@@ -1,3 +1,5 @@
this is a readme file
created by e.chia 2018/02/06
modified by e.chia 1st time
+add this to show staged version
+add this to show working directory version可以看到，git diff 比較工作區和暫存區，git diff –cache （或者–staged）比較版本和暫存區，git diff head – filename 比較branch上的head指向的版本與工作區的區別（這裡的head可以是任意指標，即用雜湊值表示的 commit id ，或者head~等）。這樣三者中的任意兩者都可以比較了。
2018-02-07 16:25:46
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