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。

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：

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：

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

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）。

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

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。

解压缩Packfile

（先删除所有objects：rm -rf objects/*)

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

跨库直接对象传输

首先创建另一个repo：

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）：

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：

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：

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：

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：

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：

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

再解bundle：

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：

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：

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：

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

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
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

(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

(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

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

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

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

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

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]

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