爲什麼git fetch指定分支不匹配沒有指定分支匹配（爲了區別）

Question

如果我做git fetch origin master做git diff ...如果我做git fetch（沒有指定分支），origin不會有相同的結果，然後做git diff ...原點（見下文）。這是爲什麼？ （只是要注意：Git版本1.7.3.1.msysgit.0）

git init parent && cd parent 

echo 'version1' > contents.txt 
git add contents.txt 
git commit -m "version1" 

cd .. 
git clone parent child 
cd child 

echo 'child' >> contents.txt 
git commit -a -m "Child" 

cd ../parent 
echo 'parent' >> contents.txt 
git commit -a -m "Parent" 

cd ../child 
git fetch origin master 
git diff ...origin 

echo Expected diff here and it wasn't there! 

git fetch 
git diff ...origin 

echo Ok, diff appeared properly now! 

Answer 1

git fetch origin master更新提交指針不存儲在.git/refs/remotes/origin/master，它存儲在.git/FETCH_HEAD，你的榜樣的輸出作爲證明：

$ git fetch origin master 
remote: Counting objects: 5, done. 
remote: Total 3 (delta 0), reused 0 (delta 0) 
Unpacking objects: 100% (3/3), done. 
From /tmp/parent 
* branch   master  -> FETCH_HEAD 

如果你想看到的差異，只是發出git diff ...FETCH_HEAD：

$ git diff ...FETCH_HEAD 
diff --git a/contents.txt b/contents.txt 
index 5bdcfc1..1f428af 100644 
--- a/contents.txt 
+++ b/contents.txt 
@@ -1 +1,2 @@ 
version1 
+parent 

你可以看到爲什麼在手冊頁：

The ref names and their object names of fetched refs are stored in .git/FETCH_HEAD. 
This information is left for a later merge operation done by git merge. 

另一方面，當您發出git fetch origin時，它會更新您的所有本地跟蹤分支。從你的例子：

$ git fetch origin 
From /tmp/parent 
e23f025..4ea3d15 master  -> origin/master 

再次從手冊頁：

Update the remote-tracking branches: 

     $ git fetch origin 

    The above command copies all branches from the remote refs/heads/ namespace and stores them to the local refs/remotes/origin/ namespace, unless the 
    branch.<name>.fetch option is used to specify a non-default refspec.