我一直在尝试添加和提交，使用diff显示HEAD、索引和工作目录之间的差异。使用diff，我的理解是它应该指定哪些文件已更改，但它也应该指定文件之间的差异（例如，如果我将"hello"写入文件中，当我运行diff并比较两个文件时，它应该说+hello（或类似的内容））。
然而，当我使用diff时，它只显示文件已更改；它未能显示这些更改是什么。为什么它没有显示文件中的具体更改——我实际添加的文本，我删除了什么等等？如果diff不能做到这一点，有没有一个命令可以用来做到呢？
谢谢。
为了进行全面测试，我删除了.git并运行了git-init，然后发现diff未显示所有三种变化的diff（git diff、git diff --cached和git diff HEAD）。我使用的文件是t.txt。下面是我的控制台输出，我对其进行了格式化以便阅读；>>是Powershell提示输入的地方，我在控制台中输入了它要求的内容；注释是我随着过程编写的，用>> # <comment>表示。
>> # Starting with nothing.
>> git status
fatal: Not a git repository (or any of the parent directories): .git
>> git init
Initialized empty Git repository in C:/Users/q/Documents/GitHub/.git/
>> ls
>> git status
On branch master
Initial commit
nothing to commit (create/copy files and use "git add" to track)
>> echo "New file created." > t.txt
>> git status
On branch master
Initial commit
Untracked files:
(use "git add <file>..." to include in what will be committed)
t.txt
nothing added to commit but untracked files present (use "git add" to track)
>> git add .
>> git status
On branch master
Initial commit
Changes to be committed:
(use "git rm --cached <file>..." to unstage)
new file: t.txt
>> #open t.txt and add a second line of text to it
>> git status
On branch master
Initial commit
Changes to be committed:
(use "git rm --cached <file>..." to unstage)
new file: t.txt
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: t.txt
>> git diff
diff --git a/t.txt b/t.txt
index e7a4f8a..fe91a49 100644
Binary files a/t.txt and b/t.txt differ
>> #How can I see the exact change?
>> #Something like: '''
>> #
>> # + This is the added line.
>> #
>> # ''' in the diff?
>> # I can take this even further by making the first commit, modifying, then staging the file
# with `git add`, then editing again, and then run all three `git-diff`s
# (git diff, git diff --cached, git diff HEAD) and none of them will specify any actual
# changes in the files; Git still just lists the files that have discrepancies, without
# listing any of the detials about /what/ is actually different.
>> git add .
>> git commit -m "Committed with the second line."
[master (root-commit) 14acc45] Committed with the second line.
1 file changed, 0 insertions(+), 0 deletions(-)
create mode 100644 t.txt
>> git diff
>> git log
commit 14acc455b16ba26cdea1661166b0ffc3fa089784
Author: q <q@gmail.com>
Date: Sat Nov 7 04:29:20 2015 -0800
Committed with the second line.
>> git diff HEAD
>> git diff HEAD^
fatal: ambiguous argument 'HEAD^': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions, like this:
'git <command> [<revision>...] -- [<file>...]'
>> #We change the file again to add a third line
>> 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: t.txt
no changes added to commit (use "git add" and/or "git commit -a")
>> git diff
diff --git a/t.txt b/t.txt
index fe91a49..006c33a 100644
Binary files a/t.txt and b/t.txt differ
>> git diff HEAD
diff --git a/t.txt b/t.txt
index fe91a49..006c33a 100644
Binary files a/t.txt and b/t.txt differ
>> git add .
>> #Modify file again.
>> git status
On branch master
Changes to be committed:
(use "git reset HEAD <file>..." to unstage)
modified: t.txt
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: t.txt
>> git diff
diff --git a/t.txt b/t.txt
index 006c33a..57a6754 100644
Binary files a/t.txt and b/t.txt differ
>> git diff HEAD
diff --git a/t.txt b/t.txt
index fe91a49..57a6754 100644
Binary files a/t.txt and b/t.txt differ
>> git diff --cached
diff --git a/t.txt b/t.txt
index fe91a49..006c33a 100644
Binary files a/t.txt and b/t.txt differ
>>## But how do they differ?