# 第5章：直接操纵远程

## 基础知识

每个repo可以引用（注意不是第0章中的“放弃对象和引用的所有权并链接”）其它repo。 这种对repo的引用称为remote。每个remote包括以下信息：

* 名字，惯例是origin和upstream
* URL，常见协议包括http、https、ftp、files、ssh（`git@github.com`实际上是ssh协议）
* 关于如何进行fetch的信息

本章所有命令都无需worktree。为了方便起见，本章所有命令都将直接在repo中操作，省略`--git-dir`。

```bash
git init --bare .
# Initialized empty Git repository in /root/
ls
# HEAD
# branches
# config
# description
# hooks
# info
# objects
# refs
```

## Packfile

研究Git remotes之前需要先研究packfile。 由于packfile内部格式相当复杂，本节不介绍Lv0命令。 以下命令均为Lv2。

在开始之前，先创建几个对象：

```bash
echo 'obj1' | git hash-object -t blob --stdin -w
# 5ff37e33c444f1ef1a6b3abda4fa05bf78352d12
echo 'obj2' | git hash-object -t blob --stdin -w
# 95fc5713e4d2debb0e898632c63bfe4a4ce0c665
echo 'obj3' | git hash-object -t blob --stdin -w
# cff99442835504ec82ba2b6d6328d898033a5300
git mktree <<EOF
100644 blob 5ff37e33c444f1ef1a6b3abda4fa05bf78352d12$(printf '\t')1.txt
100755 blob 95fc5713e4d2debb0e898632c63bfe4a4ce0c665$(printf '\t')2.txt
EOF
# 2da98740b77749cb1b6b3acaee43a3644fb3e9e5
git mktree <<EOF
100644 blob cff99442835504ec82ba2b6d6328d898033a5300$(printf '\t')3.txt
040000 tree 2da98740b77749cb1b6b3acaee43a3644fb3e9e5$(printf '\t')dir
EOF
# 187e91589a3f4f248f4cc8b1a1eca65b5161cc7b
```

检查对象创建情况：

```bash
git ls-tree -r 187e
# 100644 blob cff99442835504ec82ba2b6d6328d898033a5300    3.txt
# 100644 blob 5ff37e33c444f1ef1a6b3abda4fa05bf78352d12    dir/1.txt
# 100755 blob 95fc5713e4d2debb0e898632c63bfe4a4ce0c665    dir/2.txt
find objects -type f
# objects/5f/f37e33c444f1ef1a6b3abda4fa05bf78352d12
# objects/cf/f99442835504ec82ba2b6d6328d898033a5300
# objects/95/fc5713e4d2debb0e898632c63bfe4a4ce0c665
# objects/2d/a98740b77749cb1b6b3acaee43a3644fb3e9e5
# objects/18/7e91589a3f4f248f4cc8b1a1eca65b5161cc7b
```

### 创建Packfile

```bash
mkdir -p ../somewhere-else/
git pack-objects ../somewhere-else/prefix <<EOF
cff99442835504ec82ba2b6d6328d898033a5300
95fc5713e4d2debb0e898632c63bfe4a4ce0c665
187e91589a3f4f248f4cc8b1a1eca65b5161cc7b
EOF
# 2b2d8ce85275da98291c5ad8f60680b2dec81ba4
ls ../somewhere-else/
# prefix-2b2d8ce85275da98291c5ad8f60680b2dec81ba4.idx
# prefix-2b2d8ce85275da98291c5ad8f60680b2dec81ba4.pack
```

### 自动列出应该打包哪些对象

前述方法手工指定了打包的文件；然而，由于没有打包blob 5ff3和tree 2da9，即便接收者拿到了对象也没有什么卵用（还原不出整个tree 187e，在`git checkout-index`时会失败）。 此时需要祭出Git最复杂的Lv2命令之一：`git rev-list` （复杂程度与之不相上下的还有`git filter-branch`、`git merge-tree`）。

```bash
git rev-list --objects 187e
# 187e91589a3f4f248f4cc8b1a1eca65b5161cc7b 
# cff99442835504ec82ba2b6d6328d898033a5300 3.txt
# 2da98740b77749cb1b6b3acaee43a3644fb3e9e5 dir
# 5ff37e33c444f1ef1a6b3abda4fa05bf78352d12 dir/1.txt
# 95fc5713e4d2debb0e898632c63bfe4a4ce0c665 dir/2.txt
git rev-list --objects 187e | git pack-objects ../somewhere-else/prefix
# a451aab5615fb6d97e2ecb337b7f1d783ed66a70
```

### 查看Packfile

```bash
git verify-pack -v ../somewhere-else/prefix-2b2d8ce85275da98291c5ad8f60680b2dec81ba4.idx
# cff99442835504ec82ba2b6d6328d898033a5300 blob   5 14 12
# 95fc5713e4d2debb0e898632c63bfe4a4ce0c665 blob   5 14 26
# 187e91589a3f4f248f4cc8b1a1eca65b5161cc7b tree   63 73 40
# non delta: 3 objects
# ../somewhere-else/prefix-2b2d8ce85275da98291c5ad8f60680b2dec81ba4.pack: ok
git verify-pack -v ../somewhere-else/prefix-a451aab5615fb6d97e2ecb337b7f1d783ed66a70.idx
# 187e91589a3f4f248f4cc8b1a1eca65b5161cc7b tree   63 73 12
# cff99442835504ec82ba2b6d6328d898033a5300 blob   5 14 85
# 2da98740b77749cb1b6b3acaee43a3644fb3e9e5 tree   66 75 99
# 5ff37e33c444f1ef1a6b3abda4fa05bf78352d12 blob   5 14 174
# 95fc5713e4d2debb0e898632c63bfe4a4ce0c665 blob   5 14 188
# non delta: 5 objects
# ../somewhere-else/prefix-a451aab5615fb6d97e2ecb337b7f1d783ed66a70.pack: ok
```

对于复杂的packfile，可能出现链状结构（只保存了增量修改信息）。详情参见[这里](https://git-scm.com/book/en/v2/Git-Internals-Packfiles)。

### 解压缩Packfile

（先删除所有objects：`rm -rf objects/*`)

```bash
git unpack-objects < ../somewhere-else/prefix-a451aab5615fb6d97e2ecb337b7f1d783ed66a70.pack
```

## 跨库直接对象传输

首先创建另一个repo：

```bash
mkdir -p ../another-repo.git/objects ../another-repo.git/refs
echo 'ref: refs/heads/master' > ../another-repo.git/HEAD
# 允许直接传输对象
git config uploadpack.allowAnySHA1InWant true
git --git-dir=../another-repo.git config uploadpack.allowAnySHA1InWant true
```

直接索要对象（若不加`--keep`则直接解Packfile）：

```bash
git --git-dir=../another-repo.git fetch-pack --keep --no-progress "$(pwd)" 187e91589a3f4f248f4cc8b1a1eca65b5161cc7b
# keep    a451aab5615fb6d97e2ecb337b7f1d783ed66a70
# 187e91589a3f4f248f4cc8b1a1eca65b5161cc7b 187e91589a3f4f248f4cc8b1a1eca65b5161cc7b
```

注意：`$(pwd)`还可以是URL，用于跨域对象传输

## 跨库直接引用传输

创建引用：

```bash
git hash-object -t commit --stdin -w <<EOF
tree 187e91589a3f4f248f4cc8b1a1eca65b5161cc7b
author b1f6c1c4 <b1f6c1c4@gmail.com> 1514736000 +0800
committer b1f6c1c4 <b1f6c1c4@gmail.com> 1514736000 +0800

The commit message
EOF
# bb6d205106a1104778884986d8e3594f35170fae
git update-ref refs/heads/itst bb6d
```

直接索要引用及其对象：

```bash
git --git-dir=../another-repo.git fetch-pack --no-progress "$(pwd)" refs/heads/itst
# bb6d205106a1104778884986d8e3594f35170fae refs/heads/itst
```

直接推送引用及其对象：

```bash
git send-pack --force --no-progress ../another-repo.git refs/heads/itst
# To ../another-repo.git
#  * [new branch]      itst -> itst
```

检查远程引用：

```bash
git ls-remote ../another-repo.git
# bb6d205106a1104778884986d8e3594f35170fae    refs/heads/itst
```

## 跨库间接传输

跨域但无法建立网络连接时，先创建bundle：

```bash
git bundle create ../the-bundle refs/heads/itst
```

再解bundle：

```bash
git --git-dir=../another-repo.git bundle unbundle ../the-bundle
# bb6d205106a1104778884986d8e3594f35170fae refs/heads/itst
```

## Lv3命令

首先用Lv0命令修改设置，以讨论设置对Lv3的影响。

### 指明remote的`git push`和`git fetch`

裸remote：

```bash
cat >./config <<EOF
[remote "another"]
  url = ../another-repo.git
EOF
git push another itst
# Everything up-to-date
git fetch another itst
# From ../another-repo
#  * branch            itst       -> FETCH_HEAD
git fetch another itst:tsts
# From ../another-repo
#  * [new branch]      itst       -> tsts
```

带默认fetch的remote：

```bash
cat >./config <<EOF
[remote "another"]
  url = ../another-repo.git
  fetch = +refs/heads/*:refs/heads/abc/*
  fetch = +refs/heads/*:refs/heads/def/*
EOF
git fetch another itst
# From ../another-repo
#  * branch            itst       -> FETCH_HEAD
#  * [new branch]      itst       -> abc/itst
#  * [new branch]      itst       -> def/itst
```

强制全盘push：

```bash
cat >./config <<EOF
[remote "another"]
  url = ../another-repo.git
  mirror = true
EOF
git push another itst
# fatal: --mirror can't be combined with refspecs
git push another
# To ../another-repo.git
#  * [new branch]      abc/itst -> abc/itst
#  * [new branch]      def/itst -> def/itst
#  * [new branch]      tsts -> tsts
```

### 未指明remote的`git push`和`git fetch`

```bash
cat >./config <<EOF
[remote "another"]
  url = ../another-repo.git
[branch "itst"]
  remote = another
  merge = refs/heads/itst
EOF
git symbolic-ref HEAD refs/heads/itst
git push --verbose
# Pushing to ../another-repo.git
# To ../another-repo.git
#  = [up to date]      itst -> itst
# Everything up-to-date
# 与git fetch无关
```

```bash
cat >./config <<EOF
[remote "another"]
  url = ../another-repo.git
  fetch = +refs/heads/*:refs/remotes/another/*
[branch "itst"]
  remote = another
EOF
git symbolic-ref HEAD refs/heads/itst
git fetch --verbose
# From ../another-repo
#  * [new branch]      abc/itst   -> another/abc/itst
#  * [new branch]      def/itst   -> another/def/itst
#  * [new branch]      itst       -> another/itst
#  * [new branch]      tsts       -> another/tsts
# 与git push无关
```

### 使用Lv3命令修改设置

```bash
(rm -f ./config)
git remote add another ../another-repo.git
cat ./config
# [remote "another"]
#     url = ../another-repo.git
#     fetch = +refs/heads/*:refs/remotes/another/*
git push -u another itst
# Everything up-to-date
# Branch 'itst' set up to track remote branch 'itst' from 'another'.
cat ./config
# [remote "another"]
#     url = ../another-repo.git
#     fetch = +refs/heads/*:refs/remotes/another/*
# [branch "itst"]
#     remote = another
#     merge = refs/heads/itst
(rm -f ./config)
git remote add another --mirror=fetch ../another-repo.git
cat ./config
# [remote "another"]
#     url = ../another-repo.git
#     fetch = +refs/*:refs/*
(rm -f ./config)
git remote add another --mirror=push ../another-repo.git
cat ./config
# [remote "another"]
#     url = ../another-repo.git
#     mirror = true
```

### 关于`git pull`

`git pull`基本上是先`git fetch`再`git merge FETCH_HEAD`； `git pull --rebase`基本上是先`git fetch`再`git rebase FETCH_HEAD`。 由于这个命令高度不可控，非常不推荐使用。 然而`git pull --ff-only`却非常有用，是先`git fetch`再`git merge --ff-only FETCH_HEAD`。

## 复制repo：`git clone`

（参见第5章）

### `git clone --mirror`

复制另一个repo的大多数对象、所有普通引用、特殊引用HEAD

* Lv2

```bash
(rm -rf *) # 删掉之前所有东西
# 先准备好
git init --bare copy.git
# Initialized empty Git repository in /root/copy.git/
cat >>./copy.git/config <<EOF
[remote "origin"]
  url = git@github.com:b1f6c1c4/learn-git-the-super-hard-way.git
  fetch = +refs/*:refs/*
  mirror = true
EOF
git --git-dir=copy.git fetch origin refs/heads/master:refs/heads/master
# error: cannot run ssh: No such file or directory
# fatal: unable to fork
git --git-dir=copy.git fetch origin refs/heads/dev:refs/heads/dev
# error: cannot run ssh: No such file or directory
# fatal: unable to fork
git --git-dir=copy.git symbolic-ref HEAD refs/heads/master
```

* Lv3

```bash
rm -rf copy.git
git clone --mirror git@github.com:b1f6c1c4/learn-git-the-super-hard-way.git copy.git
# Cloning into bare repository 'copy.git'...
# error: cannot run ssh: No such file or directory
# fatal: unable to fork
```

### `git clone --bare`

与`--mirror`类似，但是四不像（没有config）

* Lv2

```bash
rm -rf copy.git
git init --bare copy.git
# Initialized empty Git repository in /root/copy.git/
tee -a ./copy.git/config <<EOF
[remote "origin"]
  url = git@github.com:b1f6c1c4/learn-git-the-super-hard-way.git
EOF
# [remote "origin"]
#   url = git@github.com:b1f6c1c4/learn-git-the-super-hard-way.git
git --git-dir=copy.git fetch origin refs/heads/master:refs/heads/master
# error: cannot run ssh: No such file or directory
# fatal: unable to fork
git --git-dir=copy.git fetch origin refs/heads/dev:refs/heads/dev
# error: cannot run ssh: No such file or directory
# fatal: unable to fork
git --git-dir=copy.git symbolic-ref HEAD refs/heads/master
```

* Lv3

```bash
rm -rf copy.git
git clone --bare git@github.com:b1f6c1c4/learn-git-the-super-hard-way.git copy.git
# Cloning into bare repository 'copy.git'...
# error: cannot run ssh: No such file or directory
# fatal: unable to fork
```

### `git clone`

* Lv2

```bash
rm -rf copy-wt
git init copy-wt
# Initialized empty Git repository in /root/copy-wt/.git/
tee -a ./copy-wt/.git/config <<EOF
[remote "origin"]
  url = git@github.com:b1f6c1c4/learn-git-the-super-hard-way.git
  fetch = +refs/*:refs/*
[branch "dev"]
  remote = origin
  merge = refs/heads/dev
EOF
# [remote "origin"]
#   url = git@github.com:b1f6c1c4/learn-git-the-super-hard-way.git
#   fetch = +refs/*:refs/*
# [branch "dev"]
#   remote = origin
#   merge = refs/heads/dev
git --git-dir=copy-wt/.git fetch origin
# error: cannot run ssh: No such file or directory
# fatal: unable to fork
git --git-dir=copy-wt/.git update-ref refs/heads/dev refs/remotes/origin/dev
# fatal: refs/remotes/origin/dev: not a valid SHA1
git --git-dir=copy-wt/.git symbolic-ref HEAD refs/heads/dev
# 如果指定了--no-checkout，省略这一行
git --git-dir=copy-wt/.git --work-tree=copy-wt checkout-index -fua
```

* Lv3

```bash
rm -rf copy-wt
git clone --branch dev git@github.com:b1f6c1c4/learn-git-the-super-hard-way.git copy-wt
# Cloning into 'copy-wt'...
# error: cannot run ssh: No such file or directory
# fatal: unable to fork
```

## 总结

* Lv2
  * Packfile
    * `git rev-list --objects <object> | git pack-objects <path-prefix>`
    * `git unpack-objects`
  * Bundle
    * `git bundle create <file> <refs>*`
    * `git bundle unbundle <file>`
  * 传输
    * `git fetch-pack <url> <hash>*` - 需要`git config uploadpack.allowAnySHA1InWant true`
    * `git fetch-pack <url> <ref>*`
    * `git send-pack --force <url> <local-ref>:<remote-ref>*`
  * 检查
    * `git ls-remote <url>`
* Lv3
  * 配置
    * `git remote add <remote> [--mirror=push|fetch] <url>`
    * `git push -u <remote> <local-ref>:<remote-ref>`
  * 传输
    * `git push <remote> <local-ref>:<remote-ref>`
    * `git fetch <remote> <remote-ref>:<local-ref>`
  * 一键跟上进度
    * `git pull --ff-only`
  * 基于远程创建repo
    * `git clone --mirror <url> <repo>`
    * `git clone --bare <url> <repo>`
    * `git clone [--no-checkout] [--branch <ref>] [--separate-git-dir <repo>] <url> <worktree>`
  * 不推荐使用的邪恶命令
    * `git pull [--rebase]`


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://b1f6c1c4.gitbook.io/learn-git-the-super-hard-way/chapter5.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.